TOC 
Network Working GroupA. Phillips, Ed.
Internet-DraftYahoo! Inc.
Obsoletes: 4646 (if approved)M. Davis, Ed.
Intended status: Best CurrentGoogle
PracticeDecember 12, 2007
Expires: June 14, 2008 


Tags for Identifying Languages
draft-ietf-ltru-4646bis-11

Status of this Memo

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Copyright Notice

Copyright © The IETF Trust (2007).

Abstract

This document describes the structure, content, construction, and semantics of language tags for use in cases where it is desirable to indicate the language used in an information object. It also describes how to register values for use in language tags and the creation of user-defined extensions for private interchange.



Table of Contents

1.  Introduction
2.  The Language Tag
    2.1.  Syntax
    2.2.  Language Subtag Sources and Interpretation
        2.2.1.  Primary Language Subtag
        2.2.2.  Extended Language Subtags
        2.2.3.  Script Subtag
        2.2.4.  Region Subtag
        2.2.5.  Variant Subtags
        2.2.6.  Extension Subtags
        2.2.7.  Private Use Subtags
        2.2.8.  Grandfathered Registrations
        2.2.9.  Classes of Conformance
3.  Registry Format and Maintenance
    3.1.  Format of the IANA Language Subtag Registry
        3.1.1.  File Format
        3.1.2.  Record Definitions
        3.1.3.  Subtag and Tag Fields
        3.1.4.  Description Field
        3.1.5.  Deprecated Field
        3.1.6.  Preferred-Value Field
        3.1.7.  Prefix Field
        3.1.8.  Suppress-Script Field
        3.1.9.  Macrolanguage Field
        3.1.10.  Comments Field
    3.2.  Language Subtag Reviewer
    3.3.  Maintenance of the Registry
    3.4.  Stability of IANA Registry Entries
    3.5.  Registration Procedure for Subtags
    3.6.  Possibilities for Registration
    3.7.  Extensions and the Extensions Registry
    3.8.  Update of the Language Subtag Registry
4.  Formation and Processing of Language Tags
    4.1.  Choice of Language Tag
    4.2.  Meaning of the Language Tag
    4.3.  Length Considerations
        4.3.1.  Working with Limited Buffer Sizes
        4.3.2.  Truncation of Language Tags
    4.4.  Canonicalization of Language Tags
    4.5.  Considerations for Private Use Subtags
5.  IANA Considerations
    5.1.  Language Subtag Registry
    5.2.  Extensions Registry
6.  Security Considerations
7.  Character Set Considerations
8.  Changes from RFC 4646
9.  References
    9.1.  Normative References
    9.2.  Informative References
Appendix A.  Acknowledgements
Appendix B.  Examples of Language Tags (Informative)
Appendix C.  Examples of Registration Forms
§  Authors' Addresses
§  Intellectual Property and Copyright Statements




 TOC 

1.  Introduction

Human beings on our planet have, past and present, used a number of languages. There are many reasons why one would want to identify the language used when presenting or requesting information.

A user's language preferences often need to be identified so that appropriate processing can be applied. For example, the user's language preferences in a Web browser can be used to select Web pages appropriately. Language preferences can also be used to select among tools (such as dictionaries) to assist in the processing or understanding of content in different languages.

In addition, knowledge about the particular language used by some piece of information content might be useful or even required by some types of processing; for example, spell-checking, computer-synthesized speech, Braille transcription, or high-quality print renderings.

One means of indicating the language used is by labeling the information content with an identifier or "tag". These tags can be used to specify user preferences when selecting information content, or for labeling additional attributes of content and associated resources.

Tags can also be used to indicate additional language attributes of content. For example, indicating specific information about the dialect, writing system, or orthography used in a document or resource may enable the user to obtain information in a form that they can understand, or it can be important in processing or rendering the given content into an appropriate form or style.

This document specifies a particular identifier mechanism (the language tag) and a registration function for values to be used to form tags. It also defines a mechanism for private use values and future extension.

This document replaces [RFC4646] (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.), which replaced [RFC3066] (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.) and its predecessor [RFC1766] (Alvestrand, H., “Tags for the Identification of Languages,” March 1995.). For a list of changes in this document, see Section 8 (Changes from RFC 4646).

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).



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2.  The Language Tag

Language tags are used to help identify languages, whether spoken, written, signed, or otherwise signaled, for the purpose of communication. This includes constructed and artificial languages, but excludes languages not intended primarily for human communication, such as programming languages.



 TOC 

2.1.  Syntax

The language tag is composed of one or more parts, known as "subtags". Each subtag consists of a sequence of alphanumeric characters. Subtags are distinguished and separated from one another by a hyphen ("-", ABNF [RFC4234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.) %x2D). A language tag consists of a "primary language" subtag and a (possibly empty) series of subsequent subtags, each of which refines or narrows the range of languages identified by the overall tag.

Usually, each type of subtag is distinguished by length, position in the tag, and content: subtags can be recognized solely by these features. The only exception to this is a fixed list of grandfathered tags registered under RFC 3066 (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.) [RFC3066]. This makes it possible to construct a parser that can extract and assign some semantic information to the subtags, even if the specific subtag values are not recognized. Thus, a parser need not have an up-to-date copy (or any copy at all) of the subtag registry to perform most searching and matching operations.



The syntax of the language tag in ABNF [RFC4234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.) is:

Language-Tag  = langtag
              / privateuse             ; private use tag
              / irregular              ; tags grandfathered by rule

langtag       = (language
                 ["-" script]
                 ["-" region]
                 *("-" variant)
                 *("-" extension)
                 ["-" privateuse])

language      = (2*3ALPHA) ; shortest ISO 639 code
              / 4ALPHA                 ; reserved for future use
              / 5*8ALPHA               ; registered language subtag

script        = 4ALPHA                 ; ISO 15924 code

region        = 2ALPHA                 ; ISO 3166 code
              / 3DIGIT                 ; UN M.49 code

variant       = 5*8alphanum            ; registered variants
              / (DIGIT 3alphanum)

extension     = singleton 1*("-" (2*8alphanum))

singleton     = %x41-57 / %x59-5A / %x61-77 / %x79-7A / DIGIT
              ; "a"-"w" / "y"-"z" / "A"-"W" / "Y"-"Z" / "0"-"9"
              ; Single alphanumerics
              ; "x" is reserved for private use

privateuse    = "x" 1*("-" (1*8alphanum))

irregular     = "en-GB-oed" / "i-ami" / "i-bnn" / "i-default"
              / "i-enochian" / "i-hak" / "i-klingon" / "i-lux"
              / "i-mingo" / "i-navajo" / "i-pwn" / "i-tao"
              / "i-tay" / "i-tsu" / "sgn-BE-fr" / "sgn-BE-nl"
              / "sgn-CH-de"

alphanum      = (ALPHA / DIGIT)       ; letters and numbers

 Figure 1: Language Tag ABNF 

All subtags have a maximum length of eight characters and whitespace is not permitted in a language tag. There is a subtlety in the ABNF production 'variant': variants starting with a digit MAY be four characters long, while those starting with a letter MUST be at least five characters long. For examples of language tags, see Appendix B (Examples of Language Tags (Informative)).

Note Well: the ABNF syntax does not distinguish between upper and lowercase. The appearance of upper and lowercase letters in the various ABNF productions above do not affect how implementations interpret tags. That is, the tag "I-AMI" matches the item "i-ami" in the 'irregular' production. At all times, the tags and their subtags, including private use and extensions, are to be treated as case insensitive: there exist conventions for the capitalization of some of the subtags, but these MUST NOT be taken to carry meaning.

For example:

However, in the tags defined by this document, the uppercase US-ASCII letters in the range 'A' through 'Z' are considered equivalent and mapped directly to their US-ASCII lowercase equivalents in the range 'a' through 'z'. Thus, the tag "mn-Cyrl-MN" is not distinct from "MN-cYRL-mn" or "mN-cYrL-Mn" (or any other combination), and each of these variations conveys the same meaning: Mongolian written in the Cyrillic script as used in Mongolia.

Although case distinctions do not carry meaning in language tags, consistent formatting and presentation of the tags will aid users. The format of the tags and subtags in the registry is RECOMMENDED. In this format, all non-initial two-letter subtags are uppercase, all non-initial four-letter subtags are titlecase, and all other subtags are lowercase.

Note that although [RFC4234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.) refers to octets, the language tags described in this document are sequences of characters from the US-ASCII [ISO646] (International Organization for Standardization, “ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.,” 1991.) repertoire. Language tags MAY be used in documents and applications that use other encodings, so long as these encompass the US-ASCII repertoire. An example of this would be an XML document that uses the UTF-16LE [RFC2781] (Hoffman, P. and F. Yergeau, “UTF-16, an encoding of ISO 10646,” February 2000.) encoding of [Unicode] (Unicode Consortium, “The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0),” January 2007.).



 TOC 

2.2.  Language Subtag Sources and Interpretation

The namespace of language tags and their subtags is administered by the Internet Assigned Numbers Authority (IANA) [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” June 2000.) according to the rules in Section 5 (IANA Considerations) of this document. The Language Subtag Registry maintained by IANA is the source for valid subtags: other standards referenced in this section provide the source material for that registry.

Terminology used in this document:

The definitions in this section apply to the various subtags within the language tags defined by this document, excepting those "grandfathered" tags defined in Section 2.2.8 (Grandfathered Registrations).

Language tags are designed so that each subtag type has unique length and content restrictions. These make identification of the subtag's type possible, even if the content of the subtag itself is unrecognized. This allows tags to be parsed and processed without reference to the latest version of the underlying standards or the IANA registry and makes the associated exception handling when parsing tags simpler.

Subtags in the IANA registry that do not come from an underlying standard can only appear in specific positions in a tag. Specifically, they can only occur as primary language subtags or as variant subtags.

Note that sequences of private use and extension subtags MUST occur at the end of the sequence of subtags and MUST NOT be interspersed with subtags defined elsewhere in this document.

Single-letter and single-digit subtags are reserved for current or future use. These include the following current uses:



 TOC 

2.2.1.  Primary Language Subtag

The primary language subtag is the first subtag in a language tag (with the exception of private use and certain grandfathered tags) and cannot be omitted. The following rules apply to the primary language subtag:

  1. All two-character primary language subtags were defined in the IANA registry according to the assignments found in the standard ISO 639 Part 1, "ISO 639-1:2002, Codes for the representation of names of languages -- Part 1: Alpha-2 code" [ISO639‑1] (International Organization for Standardization, “ISO 639-1:2002. Codes for the representation of names of languages -- Part 1: Alpha-2 code,” 2002.), or using assignments subsequently made by the ISO 639-1 registration authority (RA) or governing standardization bodies.
  2. All three-character primary language subtags were defined in the IANA registry according to the assignments found in either ISO 639 Part 2, "ISO 639-2:1998 - Codes for the representation of names of languages -- Part 2: Alpha-3 code - edition 1" [ISO639‑2] (International Organization for Standardization, “ISO 639-2:1998. Codes for the representation of names of languages -- Part 2: Alpha-3 code, first edition,” 1998.), ISO 639 Part 3, "Codes for the representation of names of languages -- Part 3: Alpha-3 code for comprehensive coverage of languages" [ISO639‑3] (International Organization for Standardization, “ISO 639-3:2007. Codes for the representation of names of languages -- Part 3: Alpha-3 code for comprehensive coverage of languages,” 2007.), or assignments subsequently made by the relevant ISO 639 registration authorities or governing standardization bodies.
  3. The subtags in the range 'qaa' through 'qtz' are reserved for private use in language tags. These subtags correspond to codes reserved by ISO 639-2 for private use. These codes MAY be used for non-registered primary language subtags (instead of using private use subtags following 'x-'). Please refer to Section 4.5 (Considerations for Private Use Subtags) for more information on private use subtags.
  4. All four-character language subtags are reserved for possible future standardization.
  5. All language subtags of 5 to 8 characters in length in the IANA registry were defined via the registration process in Section 3.5 (Registration Procedure for Subtags) and MAY be used to form the primary language subtag. At the time this document was created, there were no examples of this kind of subtag and future registrations of this type will be discouraged: primary languages are strongly RECOMMENDED for registration with ISO 639, and proposals rejected by ISO 639/RA-JAC will be closely scrutinized before they are registered with IANA.
  6. The single-character subtag 'x' as the primary subtag indicates that the language tag consists solely of subtags whose meaning is defined by private agreement. For example, in the tag "x-fr-CH", the subtags 'fr' and 'CH' SHOULD NOT be taken to represent the French language or the country of Switzerland (or any other value in the IANA registry) unless there is a private agreement in place to do so. See Section 4.5 (Considerations for Private Use Subtags).
  7. The single-character subtag 'i' is used by some grandfathered tags (see Section 2.2.8 (Grandfathered Registrations)) such as "i-klingon" and "i-bnn". (Other grandfathered tags have a primary language subtag in their first position.)
  8. Other values MUST NOT be assigned to the primary subtag except by revision or update of this document.

Note: For languages that have both an ISO 639-1 two-character code and a three character code assigned by either ISO 639-2 or ISO 639-3, only the ISO 639-1 two-character code is defined in the IANA registry.

Note: For languages that have no ISO 639-1 two-character code and for which the ISO 639-2/T (Terminology) code and the ISO 639-2/B (Bibliographic) codes differ, only the Terminology code is defined in the IANA registry. At the time this document was created, all languages that had both kinds of three-character code were also assigned a two-character code; it is expected that future assignments of this nature will not occur.

Note: To avoid problems with versioning and subtag choice as experienced during the transition between RFC 1766 and RFC 3066, as well as the canonical nature of subtags defined by this document, the ISO 639 Registration Authority Joint Advisory Committee (ISO 639/RA-JAC) has included the following statement in [iso639.prin] (ISO 639 Joint Advisory Committee, “ISO 639 Joint Advisory Committee: Working principles for ISO 639 maintenance,” March 2000.):

"A language code already in ISO 639-2 at the point of freezing ISO 639-1 shall not later be added to ISO 639-1. This is to ensure consistency in usage over time, since users are directed in Internet applications to employ the alpha-3 code when an alpha-2 code for that language is not available."

In order to avoid instability in the canonical form of tags, if a two-character code is added to ISO 639-1 for a language for which a three-character code was already included in either ISO 639-2 or ISO 639-3, the two-character code MUST NOT be registered. See Section 3.4 (Stability of IANA Registry Entries).

For example, if some content were tagged with 'haw' (Hawaiian), which currently has no two-character code, the tag would not be invalidated if ISO 639-1 were to assign a two-character code to the Hawaiian language at a later date.

Note: An example of independent primary language subtag registration might include: one of the grandfathered IANA registrations is "i-enochian". The subtag 'enochian' could be registered in the IANA registry as a primary language subtag (assuming that ISO 639 does not register this language first), making tags such as "enochian-AQ" and "enochian-Latn" valid.



 TOC 

2.2.2.  Extended Language Subtags

Extended language subtags are permanently reserved. They MUST NOT be registered or used to form language tags (except in grandfathered tags). They were originally created to allow for certain kinds of compatibility mappings which ultimately were not used.



 TOC 

2.2.3.  Script Subtag

Script subtags are used to indicate the script or writing system variations that distinguish the written forms of a language or its dialects. The following rules apply to the script subtags:

  1. Script subtags MUST follow the primary language subtag and MUST precede any other type of subtag.
  2. All four-character subtags were defined according to [ISO15924] (International Organization for Standardization, “ISO 15924:2004. Information and documentation -- Codes for the representation of names of scripts,” January 2004.)--"Codes for the representation of the names of scripts": alpha-4 script codes, or subsequently assigned by the ISO 15924 maintenance agency or governing standardization bodies, denoting the script or writing system used in conjunction with this language.
  3. The script subtags 'Qaaa' through 'Qabx' are reserved for private use in language tags. These subtags correspond to codes reserved by ISO 15924 for private use. These codes MAY be used for non-registered script values. Please refer to Section 4.5 (Considerations for Private Use Subtags) for more information on private use subtags.
  4. Script subtags MUST NOT be registered using the process in Section 3.5 (Registration Procedure for Subtags) of this document. Variant subtags MAY be considered for registration for that purpose.
  5. There MUST be at most one script subtag in a language tag, and the script subtag SHOULD be omitted when it adds no distinguishing value to the tag or when the primary language subtag's record includes a Suppress-Script field listing the applicable script subtag.

Example: "sr-Latn" represents Serbian written using the Latin script.



 TOC 

2.2.4.  Region Subtag

Region subtags are used to indicate linguistic variations associated with or appropriate to a specific country, territory, or region. Typically, a region subtag is used to indicate regional dialects or usage, or region-specific spelling conventions. A region subtag can also be used to indicate that content is expressed in a way that is appropriate for use throughout a region, for instance, Spanish content tailored to be useful throughout Latin America.

The following rules apply to the region subtags:

  1. Region subtags MUST follow any language or script subtags and MUST precede any other type of subtag.
  2. All two-character subtags following the primary subtag were defined in the IANA registry according to the assignments found in [ISO3166‑1] (International Organization for Standardization, “ISO 3166-1:2006. Codes for the representation of names of countries and their subdivisions -- Part 1: Country codes,” November 2006.) ("Codes for the representation of names of countries and their subdivisions -- Part 1: Country codes") using the list of alpha-2 country codes, or using assignments subsequently made by the ISO 3166 maintenance agency or governing standardization bodies. In addition, the codes that are "exceptionally reserved" (as opposed to "assigned") in ISO 3166-1 were also defined in the registry, with the exception of 'UK', which is an exact synonym for the assigned code 'GB'.
  3. All three-character subtags consisting of digit (numeric) characters following the primary subtag were defined in the IANA registry according to the assignments found in UN Standard Country or Area Codes for Statistical Use (Statistics Division, United Nations, “Standard Country or Area Codes for Statistical Use,” June 1999.) [UN_M.49] or assignments subsequently made by the governing standards body. Note that not all of the UN M.49 codes are defined in the IANA registry. The following rules define which codes are entered into the registry as valid subtags:
    A.
    UN numeric codes assigned to 'macro-geographical (continental)' or sub-regions MUST be registered in the registry. These codes are not associated with an assigned ISO 3166 alpha-2 code and represent supra-national areas, usually covering more than one nation, state, province, or territory.
    B.
    UN numeric codes for 'economic groupings' or 'other groupings' MUST NOT be registered in the IANA registry and MUST NOT be used to form language tags.
    C.
    UN numeric codes for countries or areas which are assigned ISO 3166 alpha2 codes already present in the registry, MUST be defined according to the rules in Section 3.4 (Stability of IANA Registry Entries) and MUST be used to form language tags that represent the country or region for which they are defined. This happens when ISO 3166 reassigns a code formerly used for one country to another.
    D.
    UN numeric codes for countries or areas for which there is an associated ISO 3166 alpha-2 code in the registry MUST NOT be entered into the registry and MUST NOT be used to form language tags. Note that the ISO 3166-based subtag in the registry MUST actually be associated with the UN M.49 code in question.
    E.
    UN numeric codes and ISO 3166 alpha-2 codes for countries or areas listed as eligible for registration in [RFC4645] (Ewell, D., Ed., “Initial Language Subtag Registry,” September 2006.) but not presently registered MAY be entered into the IANA registry via the process described in Section 3.5 (Registration Procedure for Subtags). Once registered, these codes MAY be used to form language tags.
    F.
    All other UN numeric codes for countries or areas that do not have an associated ISO 3166 alpha-2 code MUST NOT be entered into the registry and MUST NOT be used to form language tags. For more information about these codes, see Section 3.4 (Stability of IANA Registry Entries).
  4. Note: The alphanumeric codes in Appendix X of the UN document MUST NOT be entered into the registry and MUST NOT be used to form language tags. (At the time this document was created, these values matched the ISO 3166 alpha-2 codes.)
  5. There MUST be at most one region subtag in a language tag and the region subtag MAY be omitted, as when it adds no distinguishing value to the tag.
  6. The region subtags 'AA', 'QM'-'QZ', 'XA'-'XZ', and 'ZZ' are reserved for private use in language tags. These subtags correspond to codes reserved by ISO 3166 for private use. These codes MAY be used for private use region subtags (instead of using a private use subtag sequence). Please refer to Section 4.5 (Considerations for Private Use Subtags) for more information on private use subtags.

"de-CH" represents German ('de') as used in Switzerland ('CH').

"sr-Latn-RS" represents Serbian ('sr') written using Latin script ('Latn') as used in Serbia ('RS').

"es-419" represents Spanish ('es') appropriate to the UN-defined Latin America and Caribbean region ('419').



 TOC 

2.2.5.  Variant Subtags

Variant subtags are used to indicate additional, well-recognized variations that define a language or its dialects that are not covered by other available subtags. The following rules apply to the variant subtags:

  1. Variant subtags MUST follow any language, script, or region subtags, but MUST precede any extension or private use subtag sequences.
  2. Variant subtags, as a collection, are not associated with any particular external standard. The meaning of variant subtags in the registry is defined in the course of the registration process defined in Section 3.5 (Registration Procedure for Subtags). Note that any particular variant subtag might be associated with some external standard. However, association with a standard is not required for registration.
  3. More than one variant MAY be used to form the language tag.
  4. Variant subtags MUST be registered with IANA according to the rules in Section 3.5 (Registration Procedure for Subtags) of this document before being used to form language tags. In order to distinguish variants from other types of subtags, registrations MUST meet the following length and content restrictions:
    1. Variant subtags that begin with a letter (a-z, A-Z) MUST be at least five characters long.
    2. Variant subtags that begin with a digit (0-9) MUST be at least four characters long.

Variant subtag records in the language subtag registry MAY include one or more 'Prefix' fields. The 'Prefix' indicates the language tag or tags that would make a suitable prefix (with other subtags, as appropriate) in forming a language tag with the variant. That is, each of the subtags in the prefix SHOULD appear before the variant. For example, the subtag 'nedis' has a Prefix of "sl", making it suitable for forming language tags such as "sl-nedis" and "sl-IT-nedis", but not suitable for use in a tag such as "zh-nedis" or "it-IT-nedis".

"sl-nedis" represents the Natisone or Nadiza dialect of Slovenian.

"de-CH-1996" represents German as used in Switzerland and as written using the spelling reform beginning in the year 1996 C.E.

Most variants that share a prefix are mutually exclusive. For example, the German orthographic variations '1996' and '1901' SHOULD NOT be used in the same tag, as they represent the dates of different spelling reforms. A variant that can meaningfully be used in combination with another variant SHOULD include a 'Prefix' field in its registry record that lists that other variant. For example, if another German variant 'example' were created that made sense to use with '1996', then 'example' should include two Prefix fields: "de" and "de-1996".



 TOC 

2.2.6.  Extension Subtags

Extensions provide a mechanism for extending language tags for use in various applications. They are intended to identify information which is commonly used in association with languages or language tags, but which are not part of language identification. See Section 3.7 (Extensions and the Extensions Registry). The following rules apply to extensions:

  1. An extension MUST follow at least a primary language subtag. That is, a language tag cannot begin with an extension. Extensions extend language tags, they do not override or replace them. For example, "a-value" is not a well-formed language tag, while "de-a-value" is.
  2. Extension subtags are separated from the other subtags defined in this document by a single-character subtag ("singleton"). The singleton MUST be one allocated to a registration authority via the mechanism described in Section 3.7 (Extensions and the Extensions Registry) and MUST NOT be the letter 'x', which is reserved for private use subtag sequences.
  3. Note: Private use subtag sequences starting with the singleton subtag 'x' are described in Section 2.2.7 (Private Use Subtags) below.
  4. Each singleton subtag MUST appear at most one time in each tag (other than as a private use subtag). That is, singleton subtags MUST NOT be repeated. For example, the tag "en-a-bbb-a-ccc" is invalid because the subtag 'a' appears twice. Note that the tag "en-a-bbb-x-a-ccc" is valid because the second appearance of the singleton 'a' is in a private use sequence.
  5. Extension subtags MUST meet all of the requirements for the content and format of subtags defined in this document.
  6. Extension subtags MUST meet whatever requirements are set by the document that defines their singleton prefix and whatever requirements are provided by the maintaining authority.
  7. Each extension subtag MUST be from two to eight characters long and consist solely of letters or digits, with each subtag separated by a single '-'.
  8. Each singleton MUST be followed by at least one extension subtag. For example, the tag "tlh-a-b-foo" is invalid because the first singleton 'a' is followed immediately by another singleton 'b'.
  9. Extension subtags MUST follow all language, extended language, script, region, and variant subtags in a tag.
  10. All subtags following the singleton and before another singleton are part of the extension. Example: In the tag "fr-a-Latn", the subtag 'Latn' does not represent the script subtag 'Latn' defined in the IANA Language Subtag Registry. Its meaning is defined by the extension 'a'.
  11. In the event that more than one extension appears in a single tag, the tag SHOULD be canonicalized as described in Section 4.4 (Canonicalization of Language Tags).

For example, if the prefix singleton 'r' and the shown subtags were defined, then the following tag would be a valid example: "en-Latn-GB-boont-r-extended-sequence-x-private"



 TOC 

2.2.7.  Private Use Subtags

Private use subtags are used to indicate distinctions in language important in a given context by private agreement. The following rules apply to private use subtags:

  1. Private use subtags are separated from the other subtags defined in this document by the reserved single-character subtag 'x'.
  2. Private use subtags MUST conform to the format and content constraints defined in the ABNF for all subtags.
  3. Private use subtags MUST follow all language, extended language, script, region, variant, and extension subtags in the tag. Another way of saying this is that all subtags following the singleton 'x' MUST be considered private use. Example: The subtag 'US' in the tag "en-x-US" is a private use subtag.
  4. A tag MAY consist entirely of private use subtags.
  5. No source is defined for private use subtags. Use of private use subtags is by private agreement only.
  6. Private use subtags are NOT RECOMMENDED where alternatives exist or for general interchange. See Section 4.5 (Considerations for Private Use Subtags) for more information on private use subtag choice.

For example: Users who wished to utilize codes from the Ethnologue publication of SIL International for language identification might agree to exchange tags such as "az-Arab-x-AZE-derbend". This example contains two private use subtags. The first is 'AZE' and the second is 'derbend'.



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2.2.8.  Grandfathered Registrations

Prior to RFC 4646, whole language tags were registered according to the rules in RFC 1766 and/or RFC 3066. These registered tags maintain their validity. Of those tags, those that were made obsolete or redundant by the advent of RFC 4646, by this document, or by subsequent registration of subtags are maintained in the registry in records as "redundant" records. Those tags that do not match the 'langtag' production in the ABNF in this document or that contain subtags that do not individually appear in the registry are maintained in the registry in records of the "grandfathered" type.

Grandfathered tags contain one or more subtags that are not defined in the Language Subtag Registry (see Section 3 (Registry Format and Maintenance)). Redundant tags consist entirely of subtags defined above and whose independent registration was superseded by [RFC4646] (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.). For more information see Section 3.8 (Update of the Language Subtag Registry).

Some grandfathered tags are "regular" in that they match the 'langtag' production in Figure 1 (Language Tag ABNF). In some cases, these tags could become redundant if their (currently unregistered) subtags were to be registered (as variants, for example). In other cases, although the subtags match the language tag pattern, the meaning assigned to the various subtags is prohibited by rules elsewhere in this document. Those tags can never become redundant.

The remaining grandfathered tags are "irregular" and do not match the 'langtag' production. These are listed in the 'irregular' production in Figure 1 (Language Tag ABNF). These grandfathered tags can never become redundant. Many of these tags have been superseded by other registrations: their record contains a Preferred-Value field that really ought to be used to form language tags representing that value.



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2.2.9.  Classes of Conformance

Implementations sometimes need to describe their capabilities with regard to the rules and practices described in this document. Tags can be checked or verified in a number of ways, but two particular classes of tag conformance are formally defined here.

A tag is considered "well-formed" if it conforms to the ABNF (Syntax). Note that irregular grandfathered tags are now listed in the 'irregular' production.

A tag is considered "valid" if it well-formed and it also satisfies these conditions:

Note that a tag's validity depends on the date of the registry used to validate the tag. A more-recent copy of the registry might contain a subtag that an older version does not.

A tag is considered "valid" for a given extension (Extensions and the Extensions Registry) (as of a particular version, revision, and date) if it meets the criteria for "valid" above and also satisfies this condition:

Each subtag used in the extension part of the tag is valid according to the extension.

Some older implementations consider a tag "well-formed" if it matches the ABNF in [RFC4646] (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.). In that version, a well-formed tag could contain a sequence matching the obsolete 'extlang' production. Other than a few grandfathered tags (which are handled separately), no valid tags have ever matched that pattern. The difference between that ABNF and Figure 1 (Language Tag ABNF) is that the language production is replaced as follows:



obs-language  = (2*3ALPHA [ extlang ]) ; shortest ISO 639 code
              / 4ALPHA                 ; reserved for future use
              / 5*8ALPHA               ; registered language subtag

extlang       = *3("-" 3ALPHA)         ; removed in this version
 Figure 2: Obsolete Language ABNF 

Older language tag implementations sometimes reference [RFC3066] (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.). Again, all valid tags under that version also match this document's language tag ABNF. However, a wider array of tags could be considered "well-formed" under that document. The grammar used in that document was:



Language-Tag = Primary-subtag *( "-" Subtag )

Primary-subtag = 1*8ALPHA

Subtag = 1*8(ALPHA / DIGIT)
 Figure 3 



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3.  Registry Format and Maintenance

This section defines the Language Subtag Registry and the maintenance and update procedures associated with it, as well as a registry for extensions to language tags (Section 3.7 (Extensions and the Extensions Registry)).

The Language Subtag Registry contains a comprehensive list of all of the subtags valid in language tags. This allows implementers a straightforward and reliable way to validate language tags. The Language Subtag Registry will be maintained so that, except for extension subtags, it is possible to validate all of the subtags that appear in a language tag under the provisions of this document or its revisions or successors. In addition, the meaning of the various subtags will be unambiguous and stable over time. (The meaning of private use subtags, of course, is not defined by the IANA registry.)



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3.1.  Format of the IANA Language Subtag Registry

The IANA Language Subtag Registry ("the registry") is a machine-readable file in the format described in this section, plus copies of the registration forms approved in accordance with the process described in Section 3.5 (Registration Procedure for Subtags). The existing registration forms for grandfathered and redundant tags taken from RFC 3066 will be maintained as part of the obsolete RFC 3066 registry. The remaining set of subtags created by either [RFC4645] (Ewell, D., Ed., “Initial Language Subtag Registry,” September 2006.) or [registry‑update] (Ewell, D., Ed., “Update to the Language Subtag Registry,” September 2006.) will not have registration forms created for them.



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3.1.1.  File Format

The registry consists of a series of records stored in the record-jar format (described in [record‑jar] (Raymond, E., “The Art of Unix Programming,” 2003.)). Each record, in turn, consists of a series of fields that describe the various subtags and tags. The registry is a Unicode (Unicode Consortium, “The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0),” January 2007.) [Unicode] text file, using the UTF-8 (Yergeau, F., “UTF-8, a transformation format of ISO 10646,” November 2003.) [RFC3629] character encoding.

Each field can be considered a single, logical line of Unicode (Unicode Consortium, “The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0),” January 2007.) [Unicode] characters, comprising a field-name and a field-body separated by a COLON character (%x3A). Each field is terminated by the newline sequence CRLF. The text in each field MUST be in Unicode Normalization Form C (NFC).

A collection of fields forms a 'record'. Records are separated by lines containing only the sequence "%%" (%x25.25).

Although fields are logically a single line of text, each line of text in the file format is limited to 72 bytes in length. To accommodate this, the field-body can be split into a multiple-line representation; this is called "folding". Folding is always done on Unicode default grapheme boundaries (that is, never in the middle of a multibyte UTF-8 sequence nor in the middle of a combining character sequence).

Although the file format uses the UTF-8 encoding, unless otherwise indicated, fields are restricted to the printable characters from the US-ASCII (International Organization for Standardization, “ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.,” 1991.) [ISO646] repertoire.

The format of the registry is described by the following ABNF (per [RFC4234] (Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” October 2005.)):



registry   = record *("%%" CRLF record)
record     = 1*( field-name *SP ":" *SP field-body CRLF )
field-name = (ALPHA / DIGIT) [*(ALPHA / DIGIT / "-") (ALPHA / DIGIT)]
field-body = *([[*SP CRLF] 1*SP] 1*CHARS)
CHARS      = (%x21-10FFFF)      ; Unicode code points
 Figure 4: Registry Format ABNF 

The sequence '..' (%x2E.2E) in a field-body denotes a range of values. Such a range represents all subtags of the same length that are in alphabetic or numeric order within that range, including the values explicitly mentioned. For example 'a..c' denotes the values 'a', 'b', and 'c' and '11..13' denotes the values '11', '12', and '13'.

All fields whose field-body contains a date value use the "full-date" format specified in [RFC3339] (Klyne, G. and C. Newman, “Date and Time on the Internet: Timestamps,” July 2002.). For example: "2004-06-28" represents June 28, 2004, in the Gregorian calendar.



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3.1.2.  Record Definitions

There are three types of records in the registry: "File-Date", "Subtag", and "Tag" records.

The first record in the registry is a "File-Date" record. This record contains the single field whose field-name is "File-Date" (see Figure 4 (Registry Format ABNF)). The field-body of this record contains the last modification date of this copy of the registry, making it possible to compare different versions of the registry. The registry on the IANA website is the most current. Versions with an older date than that one are not up-to-date.



File-Date: 2004-06-28
%%
 Figure 5: Example of the File-Date Record 

Subsequent records represent either subtags or tags in the registry. "Subtag" records contain a field with a field-name of "Subtag", while, unsurprisingly, "Tag" records contain a field with a field-name of "Tag". Each of the fields in each record MUST occur no more than once, unless otherwise noted below. Each record MUST contain the following fields:

Each record MAY also contain the following fields:

Future versions of this document might add additional fields to the registry, so implementations SHOULD ignore fields found in the registry that are not defined in this document.



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3.1.3.  Subtag and Tag Fields

The 'Subtag' field MUST NOT use uppercase letters to form the subtag, with two exceptions. Subtags whose 'Type' field is 'script' (in other words, subtags defined by ISO 15924) MUST use titlecase. Subtags whose 'Type' field is 'region' (in other words, the non-numeric region subtags defined by ISO 3166) MUST use all uppercase. These exceptions mirror the use of case in the underlying standards.

Each subtag in the tags contained in a 'Tag' field MUST be formatted using the rules in the preceding paragraph. That is, all subtags are lowercase except for subtags that represent script or region codes.



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3.1.4.  Description Field

The field 'Description' contains a description of the tag or subtag in the record. The 'Description' field MAY appear more than once per record, that is, there can be multiple descriptions for a given record. The 'Description' field MAY include the full range of Unicode characters. At least one of the 'Description' fields MUST be written or transcribed into the Latin script; additional 'Description' fields MAY also include a description in a non-Latin script. Each 'Description' field MUST be unique, both within the record in which it appears and for the collection of records of the same type. Moreover, formatting variations of the same description MUST NOT occur in that specific record or in any other record of the same type. For example, while the ISO 639-1 code 'fy' contains both the descriptions "Western Frisian" and "Frisian, Western", only one of these descriptions appears in the registry.

The 'Description' field is used for identification purposes and SHOULD NOT be taken to represent the actual native name of the language or variation or to be in any particular language.

For subtags taken from a source standard (such as ISO 639 or ISO 3166), the 'Description' value(s) SHOULD also be taken from the source standard. Multiple descriptions in the source standard MUST be split into separate 'Description' fields. The source standard's descriptions MAY be edited, either prior to insertion or via the registration process. For fields of type 'language', the first 'Description' field appearing in the Registry corresponds to the Reference Name assigned by ISO 639-3. This helps facilitate cross-referencing between ISO 639 and the registry.

When creating or updating a record due to the action of one of the source standards, the Language Subtag Reviewer SHOULD remove duplicate or redundant descriptions and MAY edit descriptions to correct irregularities in formatting (such as misspellings, inappropriate apostrophes or other punctuation, or excessive or missing spaces) prior to submitting the proposed record to the ietf-languages list.

Note: Descriptions in registry entries that correspond to ISO 639, ISO 15924, ISO 3166, or UN M.49 codes are intended only to indicate the meaning of that identifier as defined in the source standard at the time it was added to the registry. The description does not replace the content of the source standard itself. The descriptions are not intended to be the localized English names for the subtags. Localization or translation of language tag and subtag descriptions is out of scope of this document.



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3.1.5.  Deprecated Field

The field 'Deprecated' MAY be added to any record via the maintenance process described in Section 3.3 (Maintenance of the Registry) or via the registration process described in Section 3.5 (Registration Procedure for Subtags). Usually, the addition of a 'Deprecated' field is due to the action of one of the standards bodies, such as ISO 3166, withdrawing a code. In some historical cases, it might not have been possible to reconstruct the original deprecation date. For these cases, an approximate date appears in the registry. Although valid in language tags, subtags and tags with a 'Deprecated' field are deprecated and validating processors SHOULD NOT generate these subtags. Note that a record that contains a 'Deprecated' field and no corresponding 'Preferred-Value' field has no replacement mapping.



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3.1.6.  Preferred-Value Field

The field 'Preferred-Value' contains a mapping between the record in which it appears and another tag or subtag. The value in this field is strongly RECOMMENDED as the best choice to represent the value of this record when selecting a language tag. These values form three groups:

  1. ISO 639 language codes that were later withdrawn in favor of other codes. These values are mostly a historical curiosity.
  2. ISO 3166 region codes that have been withdrawn in favor of a new code. This sometimes happens when a country changes its name or administration in such a way that warrants a new region code.
  3. Grandfathered or redundant tags from RFC 3066. In many cases, these tags have become obsolete because the values they represent were later encoded by ISO 639.

Records that contain a 'Preferred-Value' field MUST also have a 'Deprecated' field. This field contains a date of deprecation. Thus, a language tag processor can use the registry to construct the valid, non-deprecated set of subtags for a given date. In addition, for any given tag, a processor can construct the set of valid language tags that correspond to that tag for all dates up to the date of the registry. The ability to do these mappings MAY be beneficial to applications that are matching, selecting, for filtering content based on its language tags.

Note that 'Preferred-Value' mappings in records of type 'region' sometimes do not represent exactly the same meaning as the original value. There are many reasons for a country code to be changed, and the effect this has on the formation of language tags will depend on the nature of the change in question.

In particular, the 'Preferred-Value' field does not imply retagging content that uses the affected subtag.

The field 'Preferred-Value' MUST NOT be modified once created in the registry. The field MAY be added to records according to the rules in Section 3.3 (Maintenance of the Registry).

The 'Preferred-Value' field in records of type "grandfathered" and "redundant" contains whole language tags that are strongly RECOMMENDED for use in place of the record's value. In many cases, the mappings were created by deprecation of the tags during the period before this document was adopted. For example, the tag "no-nyn" was deprecated in favor of the ISO 639-1-defined language code 'nn'.



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3.1.7.  Prefix Field

The 'Prefix' field contains an extended language range whose subtags are appropriate to use with this subtag: each of the subtags in one of the subtag's Prefix fields MUST appear before the variant in a valid tag. For example, the variant subtag '1996' has a 'Prefix' field of "de". This means that tags starting with the sequence "de-" are appropriate with this subtag, so "de-Latg-1996" and "de-CH-1996" are both acceptable, while the tag "fr-1996" is an inappropriate choice.

The field of type 'Prefix' MUST NOT be removed from any record. The field-body for this type of field MAY be modified, but only if the modification broadens the meaning of the subtag. That is, the field-body can be replaced only by a prefix of itself. For example, the Prefix "be-Latn" (Belarusian, Latin script) could be replaced by the Prefix "be" (Belarusian) but not by the Prefix "ru-Latn" (Russian, Latin script).

Records of type 'variant' MAY have more than one field of type 'Prefix'. Additional fields of this type MAY be added to a 'variant' record via the registration process.

The field-body of the 'Prefix' field MUST NOT conflict with any 'Prefix' already registered for a given record. Such a conflict would occur when no valid tag could be constructed that would contain the prefix, such as when two subtags each have a 'Prefix' that contains the other subtag. For example, suppose that the subtag 'avariant' has the prefix "es-bvariant". Then the subtag 'bvariant' cannot given the prefix 'avariant', for that would require a tag of the form "es-avariant-bvariant-avariant", which would not be valid.



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3.1.8.  Suppress-Script Field

The field 'Suppress-Script' contains a script subtag (whose record appears in the registry). The field 'Suppress-Script' MUST only appear in records whose 'Type' field-body is 'language'. This field MUST NOT appear more than one time in a record. This field indicates a script used to write the overwhelming majority of documents for the given language. This script code therefore adds no distinguishing information to a language tag. This helps ensure greater compatibility between the language tags generated according to the rules in this document and language tags and tag processors or consumers based on RFC 3066 by indicating that the script subtag SHOULD NOT be used for most documents in that language. For example, virtually all Icelandic documents are written in the Latin script, making the subtag 'Latn' redundant in the tag "is-Latn".

Many language subtag records do not have a Suppress-Script field. The lack of a Suppress-Script might indicate that the language is customarily written in more than one script or that the language is not customarily written at all. It might also mean that sufficient information was not available when the record was created and thus remains a candidate for future registration.



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3.1.9.  Macrolanguage Field

The Macrolanguage field contains a primary language subtag that encompasses this subtag's language. That is, the language subtag whose record this field appears in is sometimes considered to be a sub-language of the Macrolanguage. Macrolanguage values are defined by ISO 639-3 and the exact nature of the relationship between the encompassed and encompassing languages varies on a case-by-case basis.

This field can be useful to applications or users when selecting language tags or as additional metadata useful in matching. The Macrolanguage field can only occur in records of type 'language'. Only values assigned by ISO 639-3 will be considered for inclusion. Macrolanguage fields MAY be added or removed via the normal registration process whenever ISO 639-3 defines new values or withdraws old values. Macrolanguages are informational, and MAY be removed or changed if ISO 639-3 changes the values.

For example, the language subtags 'nb' (Norwegian Bokmal) and 'nn' (Norwegian Nynorsk) each have a Macrolanguage entry of 'no' (Norwegian). For more information see Section 4.1 (Choice of Language Tag).



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3.1.10.  Comments Field

The field 'Comments' conveys additional information about the record and MAY appear more than once per record. The field-body MAY include the full range of Unicode characters and is not restricted to any particular script. This field MAY be inserted or changed via the registration process and no guarantee of stability is provided. The content of this field is not restricted, except by the need to register the information, the suitability of the request, and by reasonable practical size limitations.



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3.2.  Language Subtag Reviewer

The Language Subtag Reviewer moderates the ietf-languages mailing list, responds to requests for registration, and performs the other registry maintenance duties described in Section 3.3 (Maintenance of the Registry). Only the Language Subtag Reviewer is permitted to request IANA to change, update, or add records to the Language Subtag Registry. The Language Subtag Reviewer MAY delegate list moderation and other clerical duties as needed.

The Language Subtag Reviewer is appointed by the IESG for an indefinite term, subject to removal or replacement at the IESG's discretion. The IESG will solicit nominees for the position (upon adoption of this document or upon a vacancy) and then solicit feedback on the nominees' qualifications. Qualified candidates should be familiar with BCP 47 and its requirements; be willing to fairly, responsively, and judiciously administer the registration process; and be suitably informed about the issues of language identification so that they can draw upon and assess the claim and contributions of language experts and subtag requesters.

The subsequent performance or decisions of the Language Subtag Reviewer MAY be appealed to the IESG under the same rules as other IETF decisions (see [RFC2026] (Bradner, S., “The Internet Standards Process -- Revision 3,” October 1996.)). The IESG can reverse or overturn the decision of the Language Subtag Reviewer, provide guidance, or take other appropriate actions.



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3.3.  Maintenance of the Registry

Maintenance of the registry requires that as codes are assigned or withdrawn by ISO 639, ISO 15924, ISO 3166, and UN M.49, the Language Subtag Reviewer MUST evaluate each change and determine the appropriate course of action according to the rules in this document. Such updates follow the registration process described in Section 3.5 (Registration Procedure for Subtags). Usually the Language Subtag Reviewer will start the process for the new or updated record by filling in the registration form and submitting it. If a change to one of these standards takes place and the Language Subtag Reviewer does not do this in a timely manner, then any interested party MAY submit the form. Thereafter the registration process continues normally.

The Language Subtag Reviewer MUST ensure that new subtags meet the requirements elsewhere in this document (and most especially in Section 3.4 (Stability of IANA Registry Entries)) or submit an appropriate registration form for an alternate subtag as described in that section. Each individual subtag affected by a change MUST be sent to the ietf-languages list with its own registration form and in a separate message.



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3.4.  Stability of IANA Registry Entries

The stability of entries and their meaning in the registry is critical to the long-term stability of language tags. The rules in this section guarantee that a specific language tag's meaning is stable over time and will not change.

These rules specifically deal with how changes to codes (including withdrawal and deprecation of codes) maintained by ISO 639, ISO 15924, ISO 3166, and UN M.49 are reflected in the IANA Language Subtag Registry. Assignments to the IANA Language Subtag Registry MUST follow the following stability rules:

  1. Values in the fields 'Type', 'Subtag', 'Tag', 'Added', 'Deprecated' and 'Preferred-Value' MUST NOT be changed and are guaranteed to be stable over time.
  2. Values in the 'Description' field MUST NOT be changed in a way that would invalidate previously-existing tags. They MAY be broadened somewhat in scope, changed to add information, or adapted to the most common modern usage. For example, countries occasionally change their names; a historical example of this would be "Upper Volta" changing to "Burkina Faso".
  3. Values in the field 'Prefix' MAY be added to records of type 'variant' via the registration process. If a prefix is added to a variant record, 'Comment' fields SHOULD be used to explain different usages with the various prefixes.
  4. Values in the field 'Prefix' in records of type 'variant' MAY be modified, so long as the modifications broaden the set of prefixes. That is, a prefix MAY be replaced by one of its own prefixes. For example, the prefix "en-US" could be replaced by "en", but not by the prefixes "en-Latn", "fr", or "en-US-boont". If one of those prefixes were needed, a new Prefix SHOULD be registered.
  5. Values in the field 'Prefix' MUST NOT be removed.
  6. The field 'Comments' MAY be added, changed, modified, or removed via the registration process or any of the processes or considerations described in this section.
  7. The field 'Suppress-Script' MAY be added or removed via the registration process.
  8. The field 'Macrolanguage' MAY be added or removed via the registration process, but only in response to changes made by ISO 639. The Macrolanguage field appears whenever a language has a corresponding Macrolanguage in ISO 639. That is, the macrolanguage fields in the registry exactly match those of ISO 639. No other macrolanguage mappings will be considered for registration.
  9. Codes assigned by ISO 639-1 that do not conflict with existing two-letter primary language subtags and which have no corresponding three-letter primary or extended language subtags defined in the registry are entered into the IANA registry as new records of type 'language'.
  10. Codes assigned by ISO 639-2 that do not conflict with existing three-letter primary or extended language subtags are entered into the IANA registry as new records of type 'language'.
  11. Codes assigned by ISO 639-3 that do not conflict with existing three-letter primary language subtags are entered into the IANA registry as new primary language records.
  12. Codes assigned by ISO 15924 and ISO 3166 that do not conflict with existing subtags of the associated type and whose meaning is not the same as an existing subtag of the same type are entered into the IANA registry as new records.
  13. Codes assigned by ISO 639, ISO 15924, or ISO 3166 that are withdrawn by their respective maintenance or registration authority remain valid in language tags. A 'Deprecated' field containing the date of withdrawal MUST be added to the record. If a new record of the same type is added that represents a replacement value, then a 'Preferred-Value' field MAY also be added. The registration process MAY be used to add comments about the withdrawal of the code by the respective standard.
    Example
    The region code 'TL' was assigned to the country 'Timor-Leste', replacing the code 'TP' (which was assigned to 'East Timor' when it was under administration by Portugal). The subtag 'TP' remains valid in language tags, but its record contains the a 'Preferred-Value' of 'TL' and its field 'Deprecated' contains the date the new code was assigned ('2004-07-06').
  14. Codes assigned by ISO 639, ISO 15924, or ISO 3166 that conflict with existing subtags of the associated type, including subtags that are deprecated, MUST NOT be entered into the registry. The following additional considerations apply to subtag values that are reassigned:
    A.
    For ISO 639 codes, if the newly assigned code's meaning is not represented by a subtag in the IANA registry, the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered language subtag as an alternate value for the new code. The form of the registered language subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on language subtags in this document.
    B.
    For all subtags whose meaning is derived from an external standard (that is, by ISO 639, ISO 15924, ISO 3166, or UN M.49), if a new meaning is assigned to an existing code and the new meaning broadens the meaning of that code, then the meaning for the associated subtag MAY be changed to match. The meaning of a subtag MUST NOT be narrowed, however, as this can result in an unknown proportion of the existing uses of a subtag becoming invalid. Note: ISO 639 maintenance agency/registration authority (MA/RA) has adopted a similar stability policy.
    C.
    For ISO 15924 codes, if the newly assigned code's meaning is not represented by a subtag in the IANA registry, the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered variant subtag as an alternate value for the new code. The form of the registered variant subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on variant subtags in this document.
    D.
    For ISO 3166 codes, if the newly assigned code's meaning is associated with the same UN M.49 code as another 'region' subtag, then the existing region subtag remains as the preferred value for that region and no new entry is created. A comment MAY be added to the existing region subtag indicating the relationship to the new ISO 3166 code.
    E.
    For ISO 3166 codes, if the newly assigned code's meaning is associated with a UN M.49 code that is not represented by an existing region subtag, then the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering the appropriate UN M.49 country code as an entry in the IANA registry.
    F.
    For ISO 3166 codes, if there is no associated UN numeric code, then the Language Subtag Reviewer SHALL petition the UN to create one. If there is no response from the UN within ninety days of the request being sent, the Language Subtag Reviewer SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered variant subtag as an alternate value for the new code. The form of the registered variant subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on variant subtags in this document. This situation is very unlikely to ever occur.
  15. UN M.49 has codes for both countries and areas (such as '276' for Germany) and geographical regions and sub-regions (such as '150' for Europe). UN M.49 country or area codes for which there is no corresponding ISO 3166 code SHOULD NOT be registered, except as a surrogate for an ISO 3166 code that is blocked from registration by an existing subtag. If such a code becomes necessary, then the registration authority for ISO 3166 SHOULD first be petitioned to assign a code to the region. If the petition for a code assignment by ISO 3166 is refused or not acted on in a timely manner, the registration process described in Section 3.5 (Registration Procedure for Subtags) MAY then be used to register the corresponding UN M.49 code. This way, UN M.49 codes remain available as the value of last resort in cases where ISO 3166 reassigns a deprecated value in the registry.
  16. Stability provisions apply to grandfathered tags with this exception: should it become possible to compose one of the grandfathered tags from registered subtags, then the field 'Type' in that record is changed from 'grandfathered' to 'redundant'. Note that this will not affect language tags that match the grandfathered tag, since these tags will now match valid generative subtag sequences. For example, this document caused the ISO 639-3 code 'gan', used in the redundant tag "zh-gan", to be registered as an extended language subtag. The formerly-grandfathered tag "zh-gan" became a redundant tag as a result (but existing content or implementations that use "zh-gan" remain valid).

Note: The redundant and grandfathered entries together are the complete list of tags registered under [RFC3066] (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.). The redundant tags are those that can now be formed using the subtags defined in the registry together with the rules of Section 2.2 (Language Subtag Sources and Interpretation). The grandfathered entries include those that can never be legal under those same provisions plus those tags that contain subtags not yet registered or, perhaps, inappropriate for registration.

The set of redundant and grandfathered tags is permanent and stable: new entries in this section MUST NOT be added and existing entries MUST NOT be removed. Records of type 'grandfathered' MAY have their type converted to 'redundant'; see item 12 in Section 3.6 (Possibilities for Registration) for more information. The decision-making process about which tags were initially grandfathered and which were made redundant is described in [RFC4645] (Ewell, D., Ed., “Initial Language Subtag Registry,” September 2006.).

RFC 3066 tags that were deprecated prior to the adoption of [RFC4646] (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.) are part of the list of grandfathered tags, and their component subtags were not included as registered variants (although they remain eligible for registration). For example, the tag "art-lojban" was deprecated in favor of the language subtag 'jbo'.



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3.5.  Registration Procedure for Subtags

The procedure given here MUST be used by anyone who wants to use a subtag not currently in the IANA Language Subtag Registry.

Only subtags of type 'language' and 'variant' will be considered for independent registration of new subtags. Subtags needed for stability and subtags necessary to keep the registry synchronized with ISO 639, ISO 15924, ISO 3166, and UN M.49 within the limits defined by this document also use this process, as described in Section 3.3 (Maintenance of the Registry). Stability provisions are described in Section 3.4 (Stability of IANA Registry Entries).

This procedure MAY also be used to register or alter the information for the 'Description', 'Comments', 'Deprecated', 'Prefix', or 'Suppress-Script' fields in a subtag's record as described in Section 3.4 (Stability of IANA Registry Entries). Changes to all other fields in the IANA registry are NOT permitted.

Registering a new subtag or requesting modifications to an existing tag or subtag starts with the requester filling out the registration form reproduced below. Note that each response is not limited in size so that the request can adequately describe the registration. The fields in the "Record Requested" section SHOULD follow the requirements in Section 3.1 (Format of the IANA Language Subtag Registry).


LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester:
2. E-mail address of requester:
3. Record Requested:

   Type:
   Subtag:
   Description:
   Prefix:
   Preferred-Value:
   Deprecated:
   Suppress-Script:
   Macrolanguage:
   Comments:

4. Intended meaning of the subtag:
5. Reference to published description
   of the language (book or article):
6. Any other relevant information:

 Figure 6: The Language Subtag Registration Form 

Examples of completed registration forms can be found in Appendix C (Examples of Registration Forms) or online at http://www.iana.org/assignments/lang-subtags-templates/.

The subtag registration form MUST be sent to <ietf-languages@iana.org> for a two-week review period before it can be submitted to IANA. If modifications are made to the request during the course of the registration process (such as corrections to meet the requirements in Section 3.1 (Format of the IANA Language Subtag Registry)) the modified form MUST also be sent to <ietf-languages@iana.org> at least one week prior to submission to IANA.

Whenever an entry is created or modified in the registry, the 'File-Date' record at the start of the registry is updated to reflect the most recent modification date in the [RFC3339] (Klyne, G. and C. Newman, “Date and Time on the Internet: Timestamps,” July 2002.) "full-date" format.

Before forwarding a new registration to IANA, the Language Subtag Reviewer MUST ensure that values in the 'Subtag' field match case according to the description in Section 3.1 (Format of the IANA Language Subtag Registry).

The ietf-languages list is an open list and can be joined by sending a request to <ietf-languages-request@iana.org>. The list can be hosted by IANA or by any third party at the request of IESG.

Some fields in both the registration form as well as the registry record itself permit the use of non-ASCII characters. Registration requests SHOULD use the UTF-8 encoding for consistency and clarity. However, since some mail clients do not support this encoding, other encodings MAY be used for the registration request. The Language Subtag Reviewer is responsible for ensuring that the proper Unicode characters appear in both the archived request form and the registry record. In the case of a transcription or encoding error by IANA, the Language Subtag Reviewer will request that the registry be repaired, providing any necessary information to assist IANA.

Variant subtags are usually registered for use with a particular range of language tags. For example, the subtag 'rozaj' is intended for use with language tags that start with the primary language subtag "sl", since Resian is a dialect of Slovenian. Thus, the subtag 'rozaj' would be appropriate in tags such as "sl-Latn-rozaj" or "sl-IT-rozaj". This information is stored in the 'Prefix' field in the registry. Variant registration requests SHOULD include at least one 'Prefix' field in the registration form.

Extended language subtags MUST include exactly one 'Prefix' field.

The 'Prefix' field for a given registered subtag exists in the IANA registry as a guide to usage. Additional prefixes MAY be added by filing an additional registration form. In that form, the "Any other relevant information:" field MUST indicate that it is the addition of a prefix.

Requests to add a prefix to a variant subtag that imply a different semantic meaning will probably be rejected. For example, a request to add the prefix "de" to the subtag 'nedis' so that the tag "de-nedis" represented some German dialect would be rejected. The 'nedis' subtag represents a particular Slovenian dialect and the additional registration would change the semantic meaning assigned to the subtag. A separate subtag SHOULD be proposed instead.

The 'Description' field MUST contain a description of the tag being registered written or transcribed into the Latin script; it MAY also include a description in a non-Latin script. The 'Description' field is used for identification purposes and doesn't necessarily represent the actual native name of the language or variation or to be in any particular language.

While the 'Description' field itself is not guaranteed to be stable and errata corrections MAY be undertaken from time to time, attempts to provide translations or transcriptions of entries in the registry itself will probably be frowned upon by the community or rejected outright, as changes of this nature have an impact on the provisions in Section 3.4 (Stability of IANA Registry Entries).

When the two-week period has passed, the Language Subtag Reviewer MUST take one of the following actions:

Note that the Language Subtag Reviewer MAY raise objections on the list if he or she so desires. The important thing is that the objection MUST be made publicly.

Sometimes the request needs to be modified as a result of discussion during the review period or due to requirements in this document. The applicant, Language Subtag Reviewer, or others are free to submit a modified version of the completed registration form, which will be considered in lieu of the original request with the explicit approval of the applicant. Such changes do not restart the two-week discussion period, although an application containing the final record submitted to IANA MUST appear on the list at least one week prior to the Language Subtag Reviewer forwarding the record to IANA. The applicant is also free to modify a rejected application with additional information and submit it again; this starts a new two-week comment period.

Registrations initiated due to the provisions of Section 3.3 (Maintenance of the Registry) or Section 3.4 (Stability of IANA Registry Entries) SHALL NOT be rejected altogether (since they have to ultimately appear in the registry) and SHOULD be completed as quickly as possible. The review process allows list members to comment on the specific information in the form and the record it contains and thus help ensure that it is correct and consistent. The Language Subtag Reviewer MAY reject a specific version of the form, but MUST include in the rejection a suitable replacement, extending the review period as described above, until the form is in a format worthy of reviewer's approval.

Decisions made by the Language Subtag Reviewer MAY be appealed to the IESG [RFC2028] (Hovey, R. and S. Bradner, “The Organizations Involved in the IETF Standards Process,” October 1996.) under the same rules as other IETF decisions [RFC2026] (Bradner, S., “The Internet Standards Process -- Revision 3,” October 1996.). This includes a decision to extend the review period or the failure to announce a decision in a clear and timely manner.

The approved records appear in the Language Subtag Registry. The approved registration forms are available online under http://www.iana.org/assignments/lang-subtags-templates/.

Updates or changes to existing records follow the same procedure as new registrations. The Language Subtag Reviewer decides whether there is consensus to update the registration following the two week review period; normally, objections by the original registrant will carry extra weight in forming such a consensus.

Registrations are permanent and stable. Once registered, subtags will not be removed from the registry and will remain a valid way in which to specify a specific language or variant.

Note: The purpose of the "Reference to published description" section in the registration form is to aid in verifying whether a language is registered or what language or language variation a particular subtag refers to. In most cases, reference to an authoritative grammar or dictionary of that language will be useful; in cases where no such work exists, other well-known works describing that language or in that language MAY be appropriate. The Language Subtag Reviewer decides what constitutes "good enough" reference material. This requirement is not intended to exclude particular languages or dialects due to the size of the speaker population or lack of a standardized orthography. Minority languages will be considered equally on their own merits.



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3.6.  Possibilities for Registration

Possibilities for registration of subtags or information about subtags include:

Subtags proposed for registration that would cause all or part of a grandfathered tag to become redundant but whose meaning conflicts with or alters the meaning of the grandfathered tag MUST be rejected.

This document leaves the decision on what subtags or changes to subtags are appropriate (or not) to the registration process described in Section 3.5 (Registration Procedure for Subtags).

Note: four-character primary language subtags are reserved to allow for the possibility of alpha4 codes in some future addition to the ISO 639 family of standards.

ISO 639 defines a maintenance agency for additions to and changes in the list of languages in ISO 639. This agency is:

International Information Centre for Terminology (Infoterm)
Aichholzgasse 6/12, AT-1120
Wien, Austria
Phone: +43 1 26 75 35 Ext. 312 Fax: +43 1 216 32 72

ISO 639-2 defines a maintenance agency for additions to and changes in the list of languages in ISO 639-2. This agency is:

Library of Congress
Network Development and MARC Standards Office
Washington, D.C. 20540 USA
Phone: +1 202 707 6237 Fax: +1 202 707 0115
URL: http://www.loc.gov/standards/iso639-2

ISO 639-3 defines a maintenance agency for additions to and changes in the list of languages in ISO 639-3. This agency is:

SIL International
ISO 639-3 Registrar
7500 W. Camp Wisdom Rd.
Dallas, TX 75236 USA
Phone: +1 972 708 7400, ext. 2293 Fax: +1 972 708 7546
Email: iso639-3@sil.org
URL: http://www.sil.org/iso639-3

The maintenance agency for ISO 3166 (country codes) is:

ISO 3166 Maintenance Agency
c/o International Organization for Standardization
Case postale 56
CH-1211 Geneva 20 Switzerland
Phone: +41 22 749 72 33 Fax: +41 22 749 73 49
URL: http://www.iso.org/iso/en/prods-services/iso3166ma/index.html

The registration authority for ISO 15924 (script codes) is:

Unicode Consortium Box 391476
Mountain View, CA 94039-1476, USA
URL: http://www.unicode.org/iso15924

The Statistics Division of the United Nations Secretariat maintains the Standard Country or Area Codes for Statistical Use and can be reached at:

Statistical Services Branch
Statistics Division
United Nations, Room DC2-1620
New York, NY 10017, USA

Fax: +1-212-963-0623
E-mail: statistics@un.org
URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm



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3.7.  Extensions and the Extensions Registry

Extension subtags are those introduced by single-character subtags ("singletons") other than 'x'. They are reserved for the generation of identifiers that contain a language component and are compatible with applications that understand language tags.

The structure and form of extensions are defined by this document so that implementations can be created that are forward compatible with applications that might be created using singletons in the future. In addition, defining a mechanism for maintaining singletons will lend stability to this document by reducing the likely need for future revisions or updates.

Single-character subtags are assigned by IANA using the "IETF Consensus" policy defined by [RFC2434] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” October 1998.). This policy requires the development of an RFC, which SHALL define the name, purpose, processes, and procedures for maintaining the subtags. The maintaining or registering authority, including name, contact email, discussion list email, and URL location of the registry, MUST be indicated clearly in the RFC. The RFC MUST specify or include each of the following:

IANA will maintain a registry of allocated single-character (singleton) subtags. This registry MUST use the record-jar format described by the ABNF in Section 3.1 (Format of the IANA Language Subtag Registry). Upon publication of an extension as an RFC, the maintaining authority defined in the RFC MUST forward this registration form to iesg@ietf.org, who MUST forward the request to iana@iana.org. The maintaining authority of the extension MUST maintain the accuracy of the record by sending an updated full copy of the record to iana@iana.org with the subject line "LANGUAGE TAG EXTENSION UPDATE" whenever content changes. Only the 'Comments', 'Contact_Email', 'Mailing_List', and 'URL' fields MAY be modified in these updates.

Failure to maintain this record, maintain the corresponding registry, or meet other conditions imposed by this section of this document MAY be appealed to the IESG [RFC2028] (Hovey, R. and S. Bradner, “The Organizations Involved in the IETF Standards Process,” October 1996.) under the same rules as other IETF decisions (see [RFC2026] (Bradner, S., “The Internet Standards Process -- Revision 3,” October 1996.)) and MAY result in the authority to maintain the extension being withdrawn or reassigned by the IESG.



%%
Identifier:
Description:
Comments:
Added:
RFC:
Authority:
Contact_Email:
Mailing_List:
URL:
%%
 Figure 7: Format of Records in the Language Tag Extensions Registry 

'Identifier' contains the single-character subtag (singleton) assigned to the extension. The Internet-Draft submitted to define the extension SHOULD specify which letter or digit to use, although the IESG MAY change the assignment when approving the RFC.

'Description' contains the name and description of the extension.

'Comments' is an OPTIONAL field and MAY contain a broader description of the extension.

'Added' contains the date the RFC was published in the "full-date" format specified in [RFC3339] (Klyne, G. and C. Newman, “Date and Time on the Internet: Timestamps,” July 2002.). For example: 2004-06-28 represents June 28, 2004, in the Gregorian calendar.

'RFC' contains the RFC number assigned to the extension.

'Authority' contains the name of the maintaining authority for the extension.

'Contact_Email' contains the email address used to contact the maintaining authority.

'Mailing_List' contains the URL or subscription email address of the mailing list used by the maintaining authority.

'URL' contains the URL of the registry for this extension.

The determination of whether an Internet-Draft meets the above conditions and the decision to grant or withhold such authority rests solely with the IESG and is subject to the normal review and appeals process associated with the RFC process.

Extension authors are strongly cautioned that many (including most well-formed) processors will be unaware of any special relationships or meaning inherent in the order of extension subtags. Extension authors SHOULD avoid subtag relationships or canonicalization mechanisms that interfere with matching or with length restrictions that sometimes exist in common protocols where the extension is used. In particular, applications MAY truncate the subtags in doing matching or in fitting into limited lengths, so it is RECOMMENDED that the most significant information be in the most significant (left-most) subtags and that the specification gracefully handle truncated subtags.

When a language tag is to be used in a specific, known, protocol, it is RECOMMENDED that the language tag not contain extensions not supported by that protocol. In addition, note that some protocols MAY impose upper limits on the length of the strings used to store or transport the language tag.



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3.8.  Update of the Language Subtag Registry

Upon adoption of this document the IANA Language Subtag Registry will need an update so that it contains the complete set of subtags valid in a language tag. This collection of subtags, along with a description of the process used to create it, is described by [registry‑update] (Ewell, D., Ed., “Update to the Language Subtag Registry,” September 2006.). IANA will publish the updated version of the registry described by this document using the instructions and content of [registry‑update] (Ewell, D., Ed., “Update to the Language Subtag Registry,” September 2006.). Once published by IANA, the maintenance procedures, rules, and registration processes described in this document will be available for new registrations or updates.

Registrations that are in process under the rules defined in [RFC4646] (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.) when this document is adopted MUST be completed under the rules contained in this document.



 TOC 

4.  Formation and Processing of Language Tags

This section addresses how to use the information in the registry with the tag syntax to choose, form, and process language tags.



 TOC 

4.1.  Choice of Language Tag

The guiding principle in forming language tags is to "tag content wisely." Sometimes there is a choice between several possible tags for the same content. The choice of which tag to use depends on the content and application in question and some amount of judgment might be necessary when selecting a tag.

Interoperability is best served when the same language tag is used consistently to represent the same language. If an application has requirements that make the rules here inapplicable, then that application risks damaging interoperability. It is strongly RECOMMENDED that users not define their own rules for language tag choice.

A subtag SHOULD only be used when it adds useful distinguishing information to the tag. Extraneous subtags interfere with the meaning, understanding, and processing of language tags. In particular, users and implementations SHOULD follow the 'Prefix' and 'Suppress-Script' fields in the registry (defined in Section 3.1 (Format of the IANA Language Subtag Registry)): these fields provide guidance on when specific additional subtags SHOULD be used or avoided in a language tag.

Some applications can benefit from the use of script subtags in language tags, as long as the use is consistent for a given context. Script subtags are never appropriate for unwritten content (such as audio recordings).

Script subtags were not formally defined in [RFC3066] (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.) and their use can affect matching and subtag identification for implementations of RFC 3066, as these subtags appear between the primary language and region subtags. For example, if an implementation selects content using Basic Filtering (Phillips, A., Ed. and M. Davis, Ed., “Matching of Language Tags,” September 2006.) [RFC4647] (originally described in Section 2.5 of [RFC3066] (Alvestrand, H., “Tags for the Identification of Languages,” January 2001.)) and the user requested the language range "en-US", content labeled "en-Latn-US" will not match the request and thus not be selected. Therefore, it is important to know when script subtags will customarily be used and when they ought not be used. In the registry, the Suppress-Script field helps ensure greater compatibility between the language tags by defining when users SHOULD NOT include a script subtag with a particular primary language subtag.

The choice of subtags used to form a language tag SHOULD be guided by the following rules:

  1. Use as precise a tag as possible, but no more specific than is justified. Avoid using subtags that are not important for distinguishing content in an application.
  2. The script subtag SHOULD NOT be used to form language tags unless the script adds some distinguishing information to the tag. The field 'Suppress-Script' in the primary language record in the registry indicates script subtags that do not add distinguishing information for most applications. For example:
  3. If a tag or subtag has a 'Preferred-Value' field in its registry entry, then the value of that field SHOULD be used to form the language tag in preference to the tag or subtag in which the preferred value appears.
  4. [ISO639‑2] (International Organization for Standardization, “ISO 639-2:1998. Codes for the representation of names of languages -- Part 2: Alpha-3 code, first edition,” 1998.) has defined several codes included in the subtag registry that require additional care when choosing language tags. In most of these cases, where omitting the language tag is permitted, such omission is preferable to using these codes. Language tags SHOULD NOT incorporate these subtags as a prefix, unless the additional information conveys some value to the application.
    1. Use specific language subtags or subtag sequences in preference to subtags for language collections. A "language collection" is a subtag derived from one of the [ISO639‑2] (International Organization for Standardization, “ISO 639-2:1998. Codes for the representation of names of languages -- Part 2: Alpha-3 code, first edition,” 1998.) codes that represents multiple related languages. These codes are included as primary language subtags in the registry. For example, the code 'cmc' represents "Chamic languages". The registry contains values for each of the approximately ten individual languages represented by this collective code. Some other examples include the subtags Germanic languages ('gem') or Algonquian languages ('alg'). Since these codes are interpreted inclusively, content tagged with "en" (English), "de" (German), or "gsw" (Swiss German, Alemannic) could also (but SHOULD NOT) be tagged with "gem" (Germanic languages). Subtags derived from collection codes SHOULD NOT be used be used unless more specific language information is not available. Note that matching implementations generally do not understand the relationship between the collection and its encompassed languages, and so users ought not assume a subtag based on a language collection is a useful means for selecting content in its encompassed languages.
    2. The 'mul' (Multiple) primary language subtag identifies content in multiple languages. It SHOULD NOT be used when a list of languages (such as Content-Language) or individual tags for each content element can be used instead.
    3. The 'und' (Undetermined) primary language subtag identifies linguistic content whose language is not known. It SHOULD NOT be used unless a language tag is required and language information is not available or cannot be determined. Omitting the language tag (where permitted) is preferred. The 'und' subtag MAY be useful for protocols that require a language tag to be provided or where a primary language subtag is required (such as in "und-Latn"). The 'und' subtag MAY also be useful when matching language tags in certain situations.
    4. The 'zxx' (Non-Linguistic) primary language subtag identifies content that has no language. Some examples might include instrumental or electronic music; sound recordings consisting of nonverbal sounds; audiovisual materials with no narration, printed titles, or subtitles; machine-readable data files consisting of machine languages or character codes; or programming source code. Note: where there are fragments of linguistic content, such as programming source code containing comments written in English, the subtag 'zxx' might still be used to indicate the primary status of the content, just as 'en' can be applied to a predominantly English text that contains a few French phrases.
    5. The 'mis' (Uncoded) primary language subtag identifies content whose language is known but which does not currently have a corresponding subtag. This subtag SHOULD NOT be used. Because the addition of other codes in the future can render its application invalid, it is inherently unstable and hence incompatible with the stability goals of BCP 47. It is always preferable to use other subtags: either 'und' or (with prior agreement) private use subtags.
    6. The grandfathered tag "i-default" (Default Language) was originally registered according to [RFC1766] (Alvestrand, H., “Tags for the Identification of Languages,” March 1995.) to meet the needs of [RFC2277] (Alvestrand, H., “IETF Policy on Character Sets and Languages,” January 1998.). It is used to indicate not a specific language, but rather, it identifies the condition or content used where the language preferences of the user cannot be established. It SHOULD NOT be used except as a means of labeling the default content for applications or protocols that require default language content to be labeled with that specific tag. It MAY also be used by an application or protocol to identify when the default language content is being returned.
  5. The same variant subtag MUST NOT be used more than once within a language tag.

Some of the languages in the registry are labeled "macrolanguages" by ISO 639-3, which defines the term as "clusters of closely-related language varieties that [...] can be considered distinct individual languages, yet in certain usage contexts a single language identity for all is needed". These correspond to codes registered in ISO 639-2 as single languages that were found to correspond to more than one language in ISO 639-3. The record for each of the languages encompassed by a macrolanguage contains a 'Macrolanguage' field in the registry; the macrolanguages themselves are not specially marked.

It is always permitted, and sometimes useful, to tag an encompassed language using the subtag for its macrolanguage. However, the Macrolanguage field doesn't define what the relationship is between the encompassed language and its macrolanguage, nor does it define how languages encompassed by the same macrolanguage are related to each other. In some cases, one of the encompassed languages serves as a standard form for the entire macrolanguage and is frequently identified with it; in other cases there is no dominant language, and the macrolanguage simply serves as a cover term for the entire group.

Applications MAY use macrolanguage information to improve matching or language negotiation. For example, the information that 'sr' (Serbian) and 'hr' (Croatian) share a macrolanguage expresses a closer relation between those languages than between, say, 'sr' (Serbian) and 'ma' (Macedonian). It is valid to use either the subtag of the encompassed language or of the macrolanguage to form language tags. However, many matching applications will not be aware of the relationship between the languages. Care in selecting which subtags are used is crucial to interoperability.

In general, use the most specific subtag to form the language tag. However, where the macrolanguage tag has been historically used to denote a dominant encompassed language, it SHOULD be used in place of the subtag specific to that encompassed language unless it is necessary to clearly distinguish the macrolanguage as a whole from that enclosed dominant language variety.

In particular, the Chinese family of languages call for special consideration. Because the written form is very similar for most languages having 'zh' (Chinese) as a macrolanguage (and because historically subtags for the various encompassed languages were not available), languages such as 'yue' (Cantonese) have historically used either 'zh' or a tag (now grandfathered) beginning with 'zh'. This means that macrolanguage information can be usefully applied when searching for content or when providing fallbacks in language negotiation. For example, the information that 'yue' has a macrolangauge of 'zh' could be used in the Lookup algorithm to fallback from a request for "yue-Hans-CN" to "zh-Hans-CN" without losing the script and region information (even though the user did not specify "zh-Hans-CN" in their request).

To ensure consistent backward compatibility, this document contains several provisions to account for potential instability in the standards used to define the subtags that make up language tags. These provisions mean that no language tag created under the rules in this document will become invalid.

Standards, protocols, and applications that reference this document normatively but apply different rules to the ones given in this section MUST specify how language tag selection varies from the guidelines given here.



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4.2.  Meaning of the Language Tag

The meaning of a language tag is related to the meaning of the subtags that it contains. Each subtag, in turn, implies a certain range of expectations one might have for related content, although it is not a guarantee. For example, the use of a script subtag such as 'Arab' (Arabic script) does not mean that the content contains only Arabic characters. It does mean that the language involved is predominantly in the Arabic script. Thus a language tag and its subtags can encompass a very wide range of variation and yet remain valid in each particular instance.

Validity of a tag is not everything. While every valid tag has a meaning, it might not represent any real-world language usage. This is unavoidable in a system in which subtags can be combined freely. For example, tags such as "ar-Cyrl-CO" (Arabic, Cyrillic script, as used in Colombia ) or "tlh-Kore-AQ-fonipa" (Klingon, Korean script, as used in Antarctica, IPA phonetic transcription) are both valid and unlikely to represent a useful combination of language attributes.

The relationship between the tag and the information it identifies is defined by the context in which the tag appears. Accordingly, this section gives only possible examples of its usage.

Language tags are related when they contain a similar sequence of subtags. For example, if a language tag B contains language tag A as a prefix, then B is typically "narrower" or "more specific" than A. Thus, "zh-Hant-TW" is more specific than "zh-Hant".

This relationship is not guaranteed in all cases: specifically, languages that begin with the same sequence of subtags are NOT guaranteed to be mutually intelligible, although they might be. For example, the tag "az" shares a prefix with both "az-Latn" (Azerbaijani written using the Latin script) and "az-Cyrl" (Azerbaijani written using the Cyrillic script). A person fluent in one script might not be able to read the other, even though the text might be identical. Content tagged as "az" most probably is written in just one script and thus might not be intelligible to a reader familiar with the other script.



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4.3.  Length Considerations

There is no defined upper limit on the size of language tags. While historically most language tags have consisted of language and region subtags with a combined total length of up to six characters, larger tags have always been both possible and actually appeared in use.

Neither the language tag syntax nor other requirements in this document impose a fixed upper limit on the number of subtags in a language tag (and thus an upper bound on the size of a tag). The language tag syntax suggests that, depending on the specific language, more subtags (and thus a longer tag) are sometimes necessary to completely identify the language for certain applications; thus, it is possible to envision long or complex subtag sequences.



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4.3.1.  Working with Limited Buffer Sizes

Some applications and protocols are forced to allocate fixed buffer sizes or otherwise limit the length of a language tag. A conformant implementation or specification MAY refuse to support the storage of language tags that exceed a specified length. Any such limitation SHOULD be clearly documented, and such documentation SHOULD include what happens to longer tags (for example, whether an error value is generated or the language tag is truncated). A protocol that allows tags to be truncated at an arbitrary limit, without giving any indication of what that limit is, has the potential for causing harm by changing the meaning of tags in substantial ways.

In practice, most language tags do not require more than a few subtags and will not approach reasonably sized buffer limitations; see Section 4.1 (Choice of Language Tag).

Some specifications or protocols have limits on tag length but do not have a fixed length limitation. For example, [RFC2231] (Freed, N. and K. Moore, “MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations,” November 1997.) has no explicit length limitation: the length available for the language tag is constrained by the length of other header components (such as the charset's name) coupled with the 76-character limit in [RFC2047] (Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” November 1996.). Thus, the "limit" might be 50 or more characters, but it could potentially be quite small.

The considerations for assigning a buffer limit are:

Implementations SHOULD NOT truncate language tags unless the meaning of the tag is purposefully being changed, or unless the tag does not fit into a limited buffer size specified by a protocol for storage or transmission.

Implementations SHOULD warn the user when a tag is truncated since truncation changes the semantic meaning of the tag.

Implementations of protocols or specifications that are space constrained but do not have a fixed limit SHOULD use the longest possible tag in preference to truncation.

Protocols or specifications that specify limited buffer sizes for language tags MUST allow for language tags of up to 33 characters.

Protocols or specifications that specify limited buffer sizes for language tags SHOULD allow for language tags of at least 30 characters. Note that RFC 4646 (Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.) [RFC4646] recommended a field size of 42 character because it included the permanently reserved (and unused) 'extlang' production. The current size recommendation does not include the use of the 'extlang' field.

The following illustration shows how the 30-character recommendation was derived. The combination of language and extended language subtags was chosen for future compatibility. At up to 15 characters, this combination is longer than the longest possible primary language subtag (8 characters):



language      =  3 (ISO 639-2; ISO 639-1 requires 2)
script        =  5 (if not suppressed: see Section 4.1)
region        =  4 (UN M.49; ISO 3166 requires 3)
variant1      =  9 (needs 'language' as a prefix)
variant2      =  9 (needs 'language-variant1' as a prefix)

total         = 30 characters
 Figure 8: Derivation of the Limit on Tag Length 



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4.3.2.  Truncation of Language Tags

Truncation of a language tag alters the meaning of the tag, and thus SHOULD be avoided. However, truncation of language tags is sometimes necessary due to limited buffer sizes. Such truncation MUST NOT permit a subtag to be chopped off in the middle or the formation of invalid tags (for example, one ending with the "-" character).

This means that applications or protocols that truncate tags MUST do so by progressively removing subtags along with their preceding "-" from the right side of the language tag until the tag is short enough for the given buffer. If the resulting tag ends with a single-character subtag, that subtag and its preceding "-" MUST also be removed. For example:



Tag to truncate: zh-Latn-CN-variant1-a-extend1-x-wadegile-private1
1. zh-Latn-CN-variant1-a-extend1-x-wadegile
2. zh-Latn-CN-variant1-a-extend1
3. zh-Latn-CN-variant1
4. zh-Latn-CN
5. zh-Latn
6. zh
 Figure 9: Example of Tag Truncation 



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4.4.  Canonicalization of Language Tags

Since a particular language tag is sometimes used by many processes, language tags SHOULD always be created or generated in a canonical form.

A language tag is in canonical form when:

  1. The tag is well-formed according the rules in Section 2.1 (Syntax) and Section 2.2 (Language Subtag Sources and Interpretation).
  2. Subtags of type 'Region' that have a Preferred-Value mapping in the IANA registry (see Section 3.1 (Format of the IANA Language Subtag Registry)) SHOULD be replaced with their mapped value. Note: In rare cases, the mapped value will also have a Preferred-Value.
  3. Redundant or grandfathered tags that have a Preferred-Value mapping in the IANA registry (see Section 3.1 (Format of the IANA Language Subtag Registry)) MUST be replaced with their mapped value. These items either are deprecated mappings created before the adoption of this document (such as the mapping of "no-nyn" to "nn" or "i-klingon" to "tlh") or are the result of later registrations or additions to this document (for example, "zh-hakka" was deprecated in favor of the ISO 639-3 code 'hak' when this document was adopted).
  4. Other subtags that have a Preferred-Value mapping in the IANA registry (see Section 3.1 (Format of the IANA Language Subtag Registry)) MUST be replaced with their mapped value. These items consist entirely of clerical corrections to ISO 639-1 in which the deprecated subtags have been maintained for compatibility purposes.
  5. If more than one extension subtag sequence exists, the extension sequences are ordered into case-insensitive ASCII order by singleton subtag.

Example: The language tag "en-A-aaa-B-ccc-bbb-x-xyz" is in canonical form, while "en-B-ccc-bbb-A-aaa-X-xyz" is well-formed but not in canonical form.

Example: The language tag "en-BU" (English as used in Burma) is not canonical because the 'BU' subtag has a canonical mapping to 'MM' (Myanmar), although the tag "en-BU" maintains its validity.

Canonicalization of language tags does not imply anything about the use of upper or lowercase letters when processing or comparing subtags (and as described in Section 2.1 (Syntax)). All comparisons MUST be performed in a case-insensitive manner.

When performing canonicalization of language tags, processors MAY regularize the case of the subtags (that is, this process is OPTIONAL), following the case used in the registry. Note that this corresponds to the following casing rules: uppercase all non-initial two-letter subtags; titlecase all non-initial four-letter subtags; lowercase everything else.

Note: Case folding of ASCII letters in certain locales, unless carefully handled, sometimes produces non-ASCII character values. The Unicode Character Database file "SpecialCasing.txt" defines the specific cases that are known to cause problems with this. In particular, the letter 'i' (U+0069) in Turkish and Azerbaijani is uppercased to U+0130 (LATIN CAPITAL LETTER I WITH DOT ABOVE). Implementers SHOULD specify a locale-neutral casing operation to ensure that case folding of subtags does not produce this value, which is illegal in language tags. For example, if one were to uppercase the region subtag 'in' using Turkish locale rules, the sequence U+0130 U+004E would result instead of the expected 'IN'.

Note: if the field 'Deprecated' appears in a registry record without an accompanying 'Preferred-Value' field, then that tag or subtag is deprecated without a replacement. Validating processors SHOULD NOT generate tags that include these values, although the values are canonical when they appear in a language tag.

An extension MUST define any relationships that exist between the various subtags in the extension and thus MAY define an alternate canonicalization scheme for the extension's subtags. Extensions MAY define how the order of the extension's subtags are interpreted. For example, an extension could define that its subtags are in canonical order when the subtags are placed into ASCII order: that is, "en-a-aaa-bbb-ccc" instead of "en-a-ccc-bbb-aaa". Another extension might define that the order of the subtags influences their semantic meaning (so that "en-b-ccc-bbb-aaa" has a different value from "en-b-aaa-bbb-ccc"). However, extension specifications SHOULD be designed so that they are tolerant of the typical processes described in Section 3.7 (Extensions and the Extensions Registry).



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4.5.  Considerations for Private Use Subtags

Private use subtags, like all other subtags, MUST conform to the format and content constraints in the ABNF. Private use subtags have no meaning outside the private agreement between the parties that intend to use or exchange language tags that employ them. The same subtags MAY be used with a different meaning under a separate private agreement. They SHOULD NOT be used where alternatives exist and SHOULD NOT be used in content or protocols intended for general use.

Private use subtags are simply useless for information exchange without prior arrangement. The value and semantic meaning of private use tags and of the subtags used within such a language tag are not defined by this document.

Subtags defined in the IANA registry as having a specific private use meaning convey more information that a purely private use tag prefixed by the singleton subtag 'x'. For applications, this additional information MAY be useful.

For example, the region subtags 'AA', 'ZZ', and in the ranges 'QM'-'QZ' and 'XA'-'XZ' (derived from ISO 3166 private use codes) MAY be used to form a language tag. A tag such as "zh-Hans-XQ" conveys a great deal of public, interchangeable information about the language material (that it is Chinese in the simplified Chinese script and is suitable for some geographic region 'XQ'). While the precise geographic region is not known outside of private agreement, the tag conveys far more information than an opaque tag such as "x-someLang", which contains no information about the language subtag or script subtag outside of the private agreement.

However, in some cases content tagged with private use subtags MAY interact with other systems in a different and possibly unsuitable manner compared to tags that use opaque, privately defined subtags, so the choice of the best approach sometimes depends on the particular domain in question.



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5.  IANA Considerations

This section deals with the processes and requirements necessary for IANA to undertake to maintain the subtag and extension registries as defined by this document and in accordance with the requirements of [RFC2434] (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” October 1998.).

The impact on the IANA maintainers of the two registries defined by this document will be a small increase in the frequency of new entries or updates. IANA also is required to create a new mailing list (described below in Section 5.1 (Language Subtag Registry)) to announce registry changes and updates.



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5.1.  Language Subtag Registry

Upon adoption of this document, IANA will update the registry using instructions and content provided in a companion document: [registry‑update] (Ewell, D., Ed., “Update to the Language Subtag Registry,” September 2006.). The criteria and process for selecting the updated set of records are described in that document. The updated set of records represents no impact on IANA, since the work to create it will be performed externally.

Future work on the Language Subtag Registry includes the following activities:

Inserting or replacing whole records. These records are preformatted for IANA by the Language Subtag Reviewer, as described in Section 3.3 (Maintenance of the Registry).

Archiving and making publicly available the registration forms.

Announcing each updated version of the registry on the "ietf-languages-announcements@iana.org" mailing list.

Each registration form sent to IANA contains a single record for incorporation into the registry. The form will be sent to "iana@iana.org" by the Language Subtag Reviewer. It will have a subject line indicating whether the enclosed form represents an insertion of a new record (indicated by the word "INSERT" in the subject line) or a replacement of an existing record (indicated by the word "MODIFY" in the subject line). At no time can a record be deleted from the registry.

IANA will extract the record from the form and place the inserted or modified record into the appropriate section of the language subtag registry, grouping the records by their 'Type' field. Inserted records can be placed anywhere in the appropriate section; there is no guarantee of the order of the records beyond grouping them together by 'Type'. Modified records overwrite the record they replace.

IANA will also update the File-Date record to contain the most recent modification date when performing any inserting or modification: included in any request to insert or modify records will be a new File-Date record indicating the acceptance date of the record. This record is to be placed first in the registry, replacing the existing File-Date record. In the event that the File-Date record present in the registry has a later date than the record being inserted or modified, then the latest (most recent) record will be preserved. IANA should process multiple registration requests in order according to the File-Date in the form, since one registration could otherwise cause a more recent change to be overwritten.

The updated registry file MUST use the UTF-8 character encoding and IANA MUST check the registry file for proper encoding. Non-ASCII characters can be sent to IANA by attaching the registration form to the email message or by using various encodings in the mail message body (UTF-8 is recommended). IANA will verify any unclear or corrupted characters with the Language Subtag Reviewer prior to posting the updated registry.

IANA will also archive and make publicly available from "http://www.iana.org/assignments/lang-subtags-templates/" each registration form. Note that multiple registrations can pertain to the same record in the registry.

Developers who are dependent upon the language subtag registry sometimes would like to be informed of changes in the registry so that they can update their implementations. When any change is made to the language subtag registry, IANA will send an announcement message to "ietf-languages-announcements@iana.org" (a self-subscribing list that only IANA can post to).



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5.2.  Extensions Registry

The Language Tag Extensions Registry can contain at most 35 records and thus changes to this registry are expected to be very infrequent.

Future work by IANA on the Language Tag Extensions Registry is limited to two cases. First, the IESG MAY request that new records be inserted into this registry from time to time. These requests MUST include the record to insert in the exact format described in Section 3.7 (Extensions and the Extensions Registry). In addition, there MAY be occasional requests from the maintaining authority for a specific extension to update the contact information or URLs in the record. These requests MUST include the complete, updated record. IANA is not responsible for validating the information provided, only that it is properly formatted. It should reasonably be seen to come from the maintaining authority named in the record present in the registry.



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6.  Security Considerations

Language tags used in content negotiation, like any other information exchanged on the Internet, might be a source of concern because they might be used to infer the nationality of the sender, and thus identify potential targets for surveillance.

This is a special case of the general problem that anything sent is visible to the receiving party and possibly to third parties as well. It is useful to be aware that such concerns can exist in some cases.

The evaluation of the exact magnitude of the threat, and any possible countermeasures, is left to each application protocol (see BCP 72 (Rescorla, E. and B. Korver, “Guidelines for Writing RFC Text on Security Considerations,” July 2003.) [RFC3552] for best current practice guidance on security threats and defenses).

The language tag associated with a particular information item is of no consequence whatsoever in determining whether that content might contain possible homographs. The fact that a text is tagged as being in one language or using a particular script subtag provides no assurance whatsoever that it does not contain characters from scripts other than the one(s) associated with or specified by that language tag.

Since there is no limit to the number of variant, private use, and extension subtags, and consequently no limit on the possible length of a tag, implementations need to guard against buffer overflow attacks. See Section 4.3 (Length Considerations) for details on language tag truncation, which can occur as a consequence of defenses against buffer overflow.

Although the specification of valid subtags for an extension (see Section 3.7 (Extensions and the Extensions Registry)) MUST be available over the Internet, implementations SHOULD NOT mechanically depend on it being always accessible, to prevent denial-of-service attacks.



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7.  Character Set Considerations

The syntax in this document requires that language tags use only the characters A-Z, a-z, 0-9, and HYPHEN-MINUS, which are present in most character sets, so the composition of language tags should not have any character set issues.

Rendering of characters based on the content of a language tag is not addressed in this memo. Historically, some languages have relied on the use of specific character sets or other information in order to infer how a specific character should be rendered (notably this applies to language- and culture-specific variations of Han ideographs as used in Japanese, Chinese, and Korean). When language tags are applied to spans of text, rendering engines sometimes use that information in deciding which font to use in the absence of other information, particularly where languages with distinct writing traditions use the same characters.



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8.  Changes from RFC 4646

The main goal for this revision of this document was to incorporate ISO 639-3 and its attendant set of language codes into the IANA Language Subtag Registry, permitting the identification of many more languages and dialects than previously supported.

The specific changes in this document to meet these goals are:



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9.  References



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9.1. Normative References

[ISO15924] International Organization for Standardization, “ISO 15924:2004. Information and documentation -- Codes for the representation of names of scripts,” January 2004.
[ISO3166-1] International Organization for Standardization, “ISO 3166-1:2006. Codes for the representation of names of countries and their subdivisions -- Part 1: Country codes,” November 2006.
[ISO639-1] International Organization for Standardization, “ISO 639-1:2002. Codes for the representation of names of languages -- Part 1: Alpha-2 code,” 2002.
[ISO639-2] International Organization for Standardization, “ISO 639-2:1998. Codes for the representation of names of languages -- Part 2: Alpha-3 code, first edition,” 1998.
[ISO639-3] International Organization for Standardization, “ISO 639-3:2007. Codes for the representation of names of languages -- Part 3: Alpha-3 code for comprehensive coverage of languages,” 2007.
[ISO646] International Organization for Standardization, “ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.,” 1991.
[RFC2026] Bradner, S., “The Internet Standards Process -- Revision 3,” BCP 9, RFC 2026, October 1996.
[RFC2028] Hovey, R. and S. Bradner, “The Organizations Involved in the IETF Standards Process,” BCP 11, RFC 2028, October 1996 (TXT, HTML, XML).
[RFC2119] Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).
[RFC2277] Alvestrand, H., “IETF Policy on Character Sets and Languages,” BCP 18, RFC 2277, January 1998 (TXT, HTML, XML).
[RFC2434] Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” BCP 26, RFC 2434, October 1998 (TXT, HTML, XML).
[RFC2860] Carpenter, B., Baker, F., and M. Roberts, “Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority,” RFC 2860, June 2000.
[RFC3339] Klyne, G. and C. Newman, “Date and Time on the Internet: Timestamps,” RFC 3339, July 2002.
[RFC4234] Crocker, D. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” RFC 4234, October 2005.
[RFC4645] Ewell, D., Ed., “Initial Language Subtag Registry,” September 2006.
[RFC4647] Phillips, A., Ed. and M. Davis, Ed., “Matching of Language Tags,” September 2006.
[UN_M.49] Statistics Division, United Nations, “Standard Country or Area Codes for Statistical Use,” UN Standard Country or Area Codes for Statistical Use, Revision 4 (United Nations publication, Sales No. 98.XVII.9, June 1999.


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9.2. Informative References

[RFC1766] Alvestrand, H., “Tags for the Identification of Languages,” RFC 1766, March 1995.
[RFC2047] Moore, K., “MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text,” RFC 2047, November 1996 (TXT, HTML, XML).
[RFC2231] Freed, N. and K. Moore, “MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations,” RFC 2231, November 1997 (TXT, HTML, XML).
[RFC2781] Hoffman, P. and F. Yergeau, “UTF-16, an encoding of ISO 10646,” RFC 2781, February 2000.
[RFC3066] Alvestrand, H., “Tags for the Identification of Languages,” BCP 47, RFC 3066, January 2001.
[RFC3552] Rescorla, E. and B. Korver, “Guidelines for Writing RFC Text on Security Considerations,” BCP 72, RFC 3552, July 2003.
[RFC3629] Yergeau, F., “UTF-8, a transformation format of ISO 10646,” STD 63, RFC 3629, November 2003.
[RFC4646] Phillips, A., Ed. and M. Davis, Ed., “Tags for the Identification of Languages,” September 2006.
[Unicode] Unicode Consortium, “The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0),” January 2007.
[iso639.prin] ISO 639 Joint Advisory Committee, “ISO 639 Joint Advisory Committee: Working principles for ISO 639 maintenance,” March 2000.
[record-jar] Raymond, E., “The Art of Unix Programming,” 2003.
[registry-update] Ewell, D., Ed., “Update to the Language Subtag Registry,” September 2006.


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Appendix A.  Acknowledgements

Any list of contributors is bound to be incomplete; please regard the following as only a selection from the group of people who have contributed to make this document what it is today.

The contributors to RFC 4646, RFC 4647, RFC 3066, and RFC 1766, the precursors of this document, made enormous contributions directly or indirectly to this document and are generally responsible for the success of language tags.

The following people contributed to this document:

Stephane Bortzmeyer, Karen Broome, Peter Constable, John Cowan, Martin Duerst, Frank Ellerman, Doug Ewell, Deborah Garside, Marion Gunn, Kent Karlsson, Chris Newman, Randy Presuhn, Stephen Silver, and many, many others.

Very special thanks must go to Harald Tveit Alvestrand, who originated RFCs 1766 and 3066, and without whom this document would not have been possible.

Special thanks go to Michael Everson, who served as the Language Tag Reviewer for almost the entire RFC 1766/RFC 3066 period, as well as the Language Subtag Reviewer since the adoption of RFC 4646.

Special thanks also to Doug Ewell, for his production of the first complete subtag registry, his work to support and maintain new registrations, and his careful editorship of both RFC 4645 and [registry‑update] (Ewell, D., Ed., “Update to the Language Subtag Registry,” September 2006.).



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Appendix B.  Examples of Language Tags (Informative)

Simple language subtag:

de (German)
fr (French)
ja (Japanese)
i-enochian (example of a grandfathered tag)

Language subtag plus Script subtag:

zh-Hant (Chinese written using the Traditional Chinese script)
zh-Hans (Chinese written using the Simplified Chinese script)
sr-Cyrl (Serbian written using the Cyrillic script)
sr-Latn (Serbian written using the Latin script)

Language-Script-Region:

zh-Hans-CN (Chinese written using the Simplified script as used in mainland China)
sr-Latn-RS (Serbian written using the Latin script as used in Serbia)

Language-Variant:

sl-rozaj (Resian dialect of Slovenian)

sl-nedis (Nadiza dialect of Slovenian)

Language-Region-Variant:

de-CH-1901 (German as used in Switzerland using the 1901 variant [orthography])

sl-IT-nedis (Slovenian as used in Italy, Nadiza dialect)

Language-Script-Region-Variant:

hy-Latn-IT-arevela (Eastern Armenian written in Latin script, as used in Italy)

Language-Region:

de-DE (German for Germany)
en-US (English as used in the United States)
es-419 (Spanish appropriate for the Latin America and Caribbean region using the UN region code)

Private use subtags:

de-CH-x-phonebk
az-Arab-x-AZE-derbend

Private use registry values:

x-whatever (private use using the singleton 'x')
qaa-Qaaa-QM-x-southern (all private tags)
de-Qaaa (German, with a private script)
sr-Latn-QM (Serbian, Latin-script, private region)
sr-Qaaa-RS (Serbian, private script, for Serbia)

Tags that use extensions (examples ONLY: extensions MUST be defined by revision or update to this document or by RFC):

en-US-u-islamCal
zh-CN-a-myExt-x-private
en-a-myExt-b-another

Some Invalid Tags:

de-419-DE (two region tags)
a-DE (use of a single-character subtag in primary position; note that there are a few grandfathered tags that start with "i-" that are valid)
ar-a-aaa-b-bbb-a-ccc (two extensions with same single-letter prefix)


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Appendix C.  Examples of Registration Forms

LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester: Han Steenwijk
2. E-mail address of requester: han.steenwijk @ unipd.it
3. Record Requested:

Type:        variant
Subtag:      biske
Description: The San Giorgio dialect of Resian
Description: The Bila dialect of Resian
Prefix:      sl-rozaj
Comments:    The dialect of San Giorgio/Bila is one of the
   four major local dialects of Resian

4. Intended meaning of the subtag: The local variety of Resian as
spoken in San Giorgio/Bila

5. Reference to published description of the language (book or
article):
 -- Jan I.N. Baudouin de Courtenay - Opyt fonetiki rez'janskich
govorov, Varsava - Peterburg: Vende - Kozancikov, 1875.
LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester: Jaska Zedlik
2. E-mail address of requester: jz53 @ zedlik.com
3. Record Requested:

Type:   variant
Subtag: tarask
Description: Belarusian in Taraskievica orthography
Prefix: be
Comments: The subtag represents Branislau Taraskievic's Belarusian
  orthography as published in "Bielaruski klasycny pravapis" by Juras
  Buslakou, Vincuk Viacorka, Zmicier Sanko, and Zmicier Sauka
  (Vilnia-Miensk 2005).

4. Intended meaning of the subtag:

The subtag is intended to represent the Belarusian orthography as
published in "Bielaruski klasycny pravapis" by Juras Buslakou, Vincuk
Viacorka, Zmicier Sanko, and Zmicier Sauka (Vilnia-Miensk 2005).

5. Reference to published description of the language (book or article):

Taraskievic, Branislau. Bielaruskaja gramatyka dla skol. Vilnia: Vyd.
"Bielaruskaha kamitetu", 1929, 5th edition.

Buslakou, Juras; Viacorka, Vincuk; Sanko, Zmicier; Sauka, Zmicier.
Bielaruski klasycny pravapis. Vilnia-Miensk, 2005.

6. Any other relevant information:

Belarusian in Taraskievica orthography became widely used, especially in
Belarusian-speaking Internet segment, but besides this some books and
newspapers are also printed using this orthography of Belarusian.


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Authors' Addresses

  Addison Phillips (editor)
  Yahoo! Inc.
Email:  addison@inter-locale.com
URI:  http://www.inter-locale.com
  
  Mark Davis (editor)
  Google
Email:  mark.davis@macchiato.com or mark.davis@google.com


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Full Copyright Statement

Intellectual Property

Acknowledgment