TOC 
Network Working GroupA. Phillips, Ed.
Internet-DraftwebMethods, Inc.
Expires: April 7, 2005M. Davis
 IBM
 October 7, 2004

Tags for Identifying Languages

draft-phillips-langtags-07

Status of this Memo

This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668.

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Copyright Notice

Copyright (C) The Internet Society (2004).

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 a construct for matching such language tags, including user defined extensions for private interchange. This document replaces RFC 3066 (which replaced RFC 1766).



Table of Contents

1.  Introduction
2.  The Language Tag
    2.1  Syntax
    2.2  Language Subtag Sources and Interpretation
        2.2.1  Pre-Existing RFC 3066 Registrations
        2.2.2  Possibilities for Registration
        2.2.3  Classes of Conformance
    2.3  Choice of Language Tag
    2.4  Meaning of the Language Tag
        2.4.1  Language Range
        2.4.2  Matching Language Tags
        2.4.3  Canonicalization of Language Tags
    2.5  Considerations for Private Use Subtags
3.  IANA Considerations
    3.1  Format of the IANA Language Subtag Registry
    3.2  Stability of IANA Registry Entries
    3.3  Registration Procedure for Subtags
    3.4  Extensions and Extensions Namespace
4.  Security Considerations
5.  Character Set Considerations
6.  Changes from RFC 3066
7.  References
§  Authors' Addresses
A.  Acknowledgements
B.  Examples of Language Tags (Informative)
C.  Conversion of the RFC 3066 Language Tag Registry
§  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.

Information about a user's language preferences commonly needs to be identified so that appropriate processing can be applied. For example, the user's language preferences in a browser can be used to select web pages appropriately. A choice of language preference 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 may be useful or even required by some types of information 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 a language identifier. These identifiers can also be used to specify user preferences when selecting information content, or for labeling additional attributes of content and associated resources.

These identifiers can also be used to indicate additional attributes of content that are closely related to the language. In particular, it is often necessary to indicate specific information about the dialect, writing system, or orthography used in a document or resource, as these attributes may be important for the user to obtain information in a form that they can understand, or important in selecting appropriate processing resources for the given content.

This document specifies an identifier mechanism, a registration function for values to be used with that identifier mechanism, and a construct for matching against those values. It also defines a mechanism for private use values and future extension and describes how private use, registered values, and matching interact.

This document replaces RFC 3066, which replaced RFC 1766. For a list of changes in this document, see Section 6Changes from RFC 3066.

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119]Bradner, S., Key words for use in RFCs to Indicate Requirement Levels, March 1997.[11].



 TOC 

2. The Language Tag

2.1 Syntax

The language tag is composed of one or more parts: A primary language subtag and a (possibly empty) series of subsequent subtags. Subtags are distinguished by their length, position in the subtag sequence, and content, so that each type of subtag can be recognized solely by these features. This makes it possible to construct a parser that can extract and assign some semantic information to the subtags, even if specific subtag values are not recognized. Thus a parser need not have an up-to-date copy of the registered subtag values to perform most searching and matching operations.



The syntax of this tag in ABNF [RFC 2234]Crocker, D. and P. Overell, Augmented BNF for Syntax Specifications: ABNF, November 1997.[12] is:

Language-Tag = (lang 
                *("-" extlang)
                ["-" script] 
                ["-" region] 
                *("-" variant) 
                *("-" extension) 
                ["-" privateuse])
                / privateuse         ; private-use tag
                / grandfathered      ; grandfathered registrations

lang            = 2*3ALPHA           ; shortest ISO 639 code
                / registered-lang
extlang         = 3ALPHA             ; reserved for future use
script          = 4ALPHA             ; ISO 15924 code
region          = 2ALPHA             ; ISO 3166 code
                / 3DIGIT             ; UN country number
variant         = ALPHA (4*7alphanum) ; registered variants
                / DIGIT (3*7alphanum)                
extension       = singleton 1*("-" (2*8alphanum)) ; extension subtag(s)
privateuse      = "x" 1*("-" (1*8alphanum))       ; private use subtag(s)
singleton       = ALPHA             ; single letters 
                                    ; (except x, which has special meaning)
registered-lang = 4*8ALPHA           ; registered language subtag
grandfathered   = ALPHA *(alphanum / "-")  ; grandfathered registration
alphanum        = (ALPHA / DIGIT)    ; letters and numbers

 Figure 1: Language Tag ABNF 

The character "-" is HYPHEN-MINUS (ABNF: %x2D). Whitespace is not permitted in a language tag. Spaces in the ABNF are for legibility and are not part of the grammar. For examples of language tags, see Appendix BExamples of Language Tags (Informative). Note that although [RFC 2234]Crocker, D. and P. Overell, Augmented BNF for Syntax Specifications: ABNF, November 1997.[12] refers to octets, the language tags described in this document are sequences of characters from the US-ASCII 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 Unicode UTF-16LE encoding.

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 them, but these should not be taken to carry meaning.

For example:

However, in the language tags defined by this document, 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.

For informative examples of language tags, see Appendix BExamples of Language Tags (Informative) at the end of this document.

2.2 Language Subtag Sources and Interpretation

The namespace of language tags and their subtags is administered by the Internet Assigned Numbers Authority (IANA) [16]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 3IANA Considerations of this document. The registry maintained by IANA is the source for valid subtags: other standards referenced in this section provide the source material for that registry.

Terminology in this section:

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 2.2.1Pre-Existing RFC 3066 Registrations.

Language tags are designed so that each subtag 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 digit subtags are reserved for current or future use. These include the following current uses:

The primary subtag is the first subtag in a language tag and cannot be empty. Except as noted, the primary subtag is the language subtag. The following rules apply to the assignment and interpretation of the primary subtag:

Note: For languages that have both an ISO 639-1 2-character code and an ISO 639-2 3-character code, only the ISO 639-1 2-character code is defined in the IANA registry.

Note: For languages that have no ISO 639-1 2-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 3-character code were also assigned a 2-character code; it is not expected that future assignments of this nature will 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 [6]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 of the canonical form of tags, if a 2-character code is added to ISO 639-1 for a language for which a 3-character code was already included in ISO 639-2, the 2-character code will not be added as a subtag in the registry. See Section 3.2Stability of IANA Registry Entries.

For example, if some content were tagged with 'haw' (Hawaiian), which currently has no 2-character code, the tag would not be invalidated if ISO 639-1 were to assign a 2-character code to the Hawaiian language at a later date.

For example, 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.

The following rules apply to the extended language subtags:

Example: In a future revision or update of this document, the tag "zh-gan" (registered under RFC 3066) might become a valid non-grandfathered tag in which the subtag 'gan' might represent the Chinese dialect 'Gan'.

The following rules apply to the script subtags:

Example: "de-Latn" represents German written using the Latin script.

The following rules apply to the region subtags:

"de-Latn-CH" represents German ('de') written using the Latin script ('Latn') as used in Switzerland ('CH').

"sr-Latn-YU" represents Serbian ('sr') written using Latin script ('Latn') as used in Serbia and Montenegro ('YU'). Note: Stability rules described in Section 3.2Stability of IANA Registry Entries apply to this language tag).

"es-419" represents Spanish ('es') as used in the UN-defined Latin America and Caribbean region ('419').

The following rules apply to the variant subtags:

"en-boont" represents the Boontling dialect of English.

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

The following rules apply to extensions:

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"

The following rules apply to private-use subtags:

For example: Users who wished to utilize SIL Ethnologue for 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'.

2.2.1 Pre-Existing RFC 3066 Registrations

Existing IANA-registered language tags from RFC 1766 and/or RFC 3066 that are not defined by additions to this document maintain their validity. IANA will maintain these tags in the registry under either the "grandfathered" or "redundant" type. For more information see Appendix CConversion of the RFC 3066 Language Tag Registry.

2.2.2 Possibilities for Registration

Possibilities for registration of subtags include:

This document leaves the decision on what subtags are appropriate or not to the registration process described in Section 3.3Registration Procedure for Subtags.

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

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

2.2.3 Classes of Conformance

Implementations may wish to express their level of conformance with the rules and practices described in this document. There are generally two classes of conforming implementations: "well-formed" processors and "validating" processors. Claims of conformance SHOULD explicitly reference one of these definitions.

An implementation that claims to check for well-formed language tags MUST:

Well-formed processors are strongly encouraged to implement the default fallback mechanism in Section 2.4.2Matching Language Tags and the associated canonicalization rules contained in Section 2.4.3Canonicalization of Language Tags.

An implementation that claims to be validating MUST:

2.3 Choice of Language Tag

One may occasionally be faced with several possible tags for the same body of text.

Interoperability is best served when all users use the same language tag in order to represent the same language. If an application has requirements that make the rules here inapplicable, then that application risks damaging interoperability. Users of this document are strongly discouraged against defining their own rules for language tag choice and matching.

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

  1. Use as precise a tag as possible, but no more specific than is justified. For example, 'de' might suffice for tagging an email written in German, while "de-CH-1996" is probably unnecessarily precise for such a task.
  2. Avoid using subtags that add no distinguishing information about the content. For example, the script subtag in "en-Latn-US" is generally unnecessary, since nearly all English texts are written in the Latin script.
  3. Use the canonical subtag from the IANA registry in preference to any of its aliases. For example, you SHOULD use 'he' for Hebrew in preference to 'iw'.
  4. You SHOULD NOT use the 'UND' (Undetermined) language subtag to label content, even if the language is unknown. Omitting the tag is preferred. Some protocols may force you to give a value for the language tag and the 'UND' subtag may be useful when specifying a range (as described in Section 2.4.2Matching Language Tags).
  5. You SHOULD NOT use the 'MUL' (Multiple) subtag if the protocol allows you to use multiple languages, as is the case for the Content-Language header in HTTP.

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 obsolete. In addition, tags that are in canonical form will always be in canonical form.

2.4 Meaning of the Language Tag

The language tag always defines a language as spoken (or written, signed or otherwise signaled) by human beings for communication of information to other human beings. Computer languages such as programming languages are explicitly excluded.

If a language tag B contains language tag A as a prefix, then B is typically "narrower" or "more specific" than A. For example, "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 may 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 may 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.

The relationship between the tag and the information it relates to is defined by the standard describing the context in which it appears. Accordingly, this section can only give possible examples of its usage.

2.4.1 Language Range

A Language Range is a set of languages whose tags all begin with the same sequence of subtags. A Language Range can be represented by a 'language-range' tag, by using the definition from HTTP/1.1Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, Hypertext Transfer Protocol -- HTTP/1.1, June 1999.[15] :

language-range = language-tag / "*"

That is, a language-range has the same syntax as a language-tag or is the single character "*". This definition of language-range implies that there is a semantic relationship between tags that share the same subtag prefixes.

A language-range matches a language-tag if it exactly equals the tag, or if it exactly equals a prefix of the tag such that the first character following the prefix is "-". (That is, the language-range "en-de" matches the language tag "en-DE-boont", but not the language tag "en-Deva".)

The special range "*" matches any tag. A protocol which uses language ranges may specify additional rules about the semantics of "*"; for instance, HTTP/1.1 specifies that the range "*" matches only languages not matched by any other range within an "Accept-Language:" header.

As noted above, not all languages or content denoted by a specific language-range may be mutually intelligible and this use of a prefix matching rule does not imply that language tags are assigned to languages in such a way that it is always true that if a user understands a language with a certain tag, then this user will also understand all languages with tags for which this tag is a prefix. The prefix rule simply allows the use of prefix tags if this is the case.

2.4.2 Matching Language Tags

Implementations that are searching for content or otherwise matching language tags to a language-range [Section 2.4.1Language Range] may choose to assume that there is a semantic relationship between two tags that share common prefixes. This is called 'language tag fallback'. The most common implementation follows this pattern:

  1. When searching for content using language tag fallback, the language tag is progressively truncated from the end until a match is located. For example, starting with the tag "en-US-boont", searches or matches would first be performed with the whole tag, then with "en-US", and finally with "en". This allows some flexibility in finding content in accordance with Rules 1 and 2 in Section 2.3Choice of Language Tag. It also typically provides better results when data is not available at a specific level of tag granularity or is sparsely populated (than if the default language for the system or content were used). Any implementation that uses this technique should ensure that appropriate data is available on each level.

    Tag to match: en-US-boont
    1. en-US-boont
    2. en-US
    3. en
      
     Figure 2: Default Fallback Pattern Example 

  2. Note:
    Implementations may choose to implement different styles of matching for different kinds of processing. For example, an implementation could treat an absent script subtag as a "wildcard" field; thus "az-AZ" would match "az-AZ", "az-Cyrl-AZ", "az-Latn-AZ", etc. but not "az". If one item is to be chosen, the implementation could pick among those matches based on other information, such as the most likely script used in the language/region in question. Because the language subtag cannot be absent, the 'UND' subtag can sometimes be used as a 'wildcard' for this style of matching. For example, in a query where you want to select all language tags that contain 'Latn' as the script code and 'AZ' as the region code, you could use "und-Latn-AZ".
    Note:
    Private-use and Extension subtags are orthogonal to language tag fallback. By default, implementations SHOULD ignore both private-use and extension subtags and follow the default fallback pattern (above). Thus a request to match the tag "en-US-boont-x-1943" would produce exactly the same information content as the example above.
  3. Implementations that choose to interpret one or more private-use or extension subtags can choose a different fallback pattern or use the private-use or extension subtags to interpret content in a different fashion.
  4. Implementations that choose not to interpret one or more private-use or extension subtags SHOULD NOT remove or modify these extensions in content that they are processing.
  5. Any language tag processor MAY match language tags using simple string comparisons and the default fallback pattern and SHOULD use this pattern for unrecognized extension subtag sequences that are processed for matching. When performing canonicalization of language tags for the purpose of matching, implementations MUST NOT reorder the subtags within an extension or private-use subtag sequence.
  6. Extension and private-use subtags MAY be ignored when matching or comparing language tags to a language-range (such as when performing language negotiation or selecting content).
  7. Some applications of language tags may want or need to consider extensions and private-use subtags when matching tags. If extensions and private-use subtags are included in a matching process that utilizes the default fallback mechanism, then the implementation MUST canonicalize the language tags and/or ranges before performing the matching. Note that implementations that claim to be "well-formed" processors as defined in Section 2.2.3Classes of Conformance generally fall into this category.

2.4.3 Canonicalization of Language Tags

Since a particular language tag or language-range may be processed many times, language tags SHOULD always be created or generated in a canonical form suitable for matching using the default fallback mechanism.

A language tag is in canonical form when:

  1. The tag is well-formed according the rules in Section 2.1Syntax and Section 2.2Language Subtag Sources and Interpretation.
  2. None of the subtags in the language tag has a canonical_value mapping in the IANA registry (see Section 3.1Format of the IANA Language Subtag Registry). Subtags with a canonical_value mapping must be replaced with their mapping in order to canonicalize the tag.
  3. 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-NH" (English as used in the New Hebrides) is not canonical because the 'NH' subtag has a canonical mapping to 'VU' (Vanuatu).

Note: Canonicalization of language tags does not imply anything about the use of upper or lowercase letter in subtags as described in Section 2.1Syntax. All comparisons MUST be performed in a case-insensitive manner.

An extension MUST define any relationships that may 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").

2.5 Considerations for Private Use Subtags

Private-use subtags require private agreement between the parties that intend to use or exchange language tags that use them and great caution should be used in employing them 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.

The use of 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 may depend on the particular domain in question.



 TOC 

3. IANA Considerations

This section deals with the processes and requirements necessary to maintain the registry of subtags and extensions for use in language tags as defined by this document and in accordance with the requirements of RFC 2434Narten, T. and H. Alvestrand, Guidelines for Writing an IANA Considerations Section in RFCs, October 1998.[14].

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.)

The registry defined under this document 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.

3.1 Format of the IANA Language Subtag Registry

The IANA Language Subtag Registry will consist of a text file that is machine readable in the format described in this section, plus copies of the registration forms approved by the Language Subtag Reviewer in accordance with the process described in Section 3.3Registration Procedure for Subtags. With the exception of the registration forms for grandfathered tags, no registration records will be maintained for the initial set of subtags.

Each record in the subtag registry will consist of a series of fields separated by semicolons and terminated by a newline. Text appearing after a "#" symbol contains comments. Whitespace surrounding fields in the file is ignored. Lists inside a field are comma separated.

There is a single date record at the start of the file which indicates the most recent modification date of the file. It has two fields: the type field is "date", and the second field is the modification date, in ISO 8601 format. For example: 2004-06-28 represents June 28, 2004 in the Gregorian calendar:

date; 2004-06-28

The fields in each subtag record, in order, are:

type; subtag; description; date; canonical_value; recommended_prefix # comments

The field 'type' MUST consist of one of the following strings: "language", "extlang", "script", "region", "variant", "grandfathered", and "redundant" and denotes the type of subtag (or tag, in the case of "grandfathered" and "redundant").

The field 'subtag' contains the subtag being defined.

The field 'description' contains a description of the subtag transcribed into ASCII.

The field 'date' contains the date the record was added to the registry in ISO 8601 format. For example: 2004-06-28 represents June 28, 2004, in the Gregorian calendar.

The field 'canonical value' represents a canonical mapping of this record to a subtag record of the same 'type'. Note that this field SHALL NOT be modified (except for records of type "grandfathered"): therefore a subtag whose record contains no canonical mapping when the record is created is a canonical form and will remain so.

The field 'recommended prefix' is for use with registered variants and contains a comma separated list of language-ranges considered most appropriate for use with this subtag. Additional values can be added to this field for variants only via additional registration. Other modification of this field (such as removing or changing values) is not permitted.

Notes and comments may contain additional information about the subtag, as deemed appropriate for understanding the registry and implementing language tags using the various subtags. These values can be changed via the registration process and no guarantee of stability is provided.



# IANA Language Subtag Registry
# This registry lists all valid subtags for language tags
# created under RFC XXXX.
date; 2004-08-07

# language codes: ISO 639 and registered codes

# ISO 639-1 (alpha-2) codes
language; aa; Afar; 2004-07-06; ;
language; ab; Abkhazian; 2004-07-06; ;
language; ae; Avestan; 2004-07-06; ;
language; he; hebrew; 2004-06-28; ;
language; iw; hebrew; 2004-06-28; he ; #note mapping
language; qaa..qtz; PRIVATE USE; 2004-07-06; ;
language; raj; Rajasthani; 2004-07-06; ;
language; seuss; Hypothetical Language; 2005-04-01 ; ;# registered language

# script codes: ISO 15924

script; Arab; Arabic; 2004-07-06; ;
script; Armn; Armenian; 2004-07-06; ;
script; Bali; Balinese; 2004-07-06; ;
# region codes: ISO 3166 and UN codes

# ISO 3166-1 alpha-2 codes

region; AA; PRIVATE USE; 2004-08-01; ;
region; AD; Andorra; 2004-07-06; ;
region; AE; United Arab Emirates; 2004-07-06; ;
region; AF; Afghanistan; 2004-07-06; ;
region; CS; Czechoslovakia; 2004-06-28; ;
region; YU; Serbia and Montenegro; 2004-06-28; ;# changed 2003-07-23;  formerly Yugoslavia

# United Nations M.49 numeric codes
region; 001; World; 2004-07-06; ;
region; 002; Africa; 2004-07-06; ;
region; 003; North America; 2004-07-06; ;
region; 005; South America; 2004-07-06; ;

## registered variants

variant; boont; Boontling; 2003-02-14; ; en
variant; gaulish; Gaulish; 2001-05-25; ; cel
variant; guoyu; Mandarin or Standard Chinese; 1999-12-18; ; zh

# grandfathered from RFC 3066

grandfathered; en-GB-oed; English, Oxford English Dictionary spelling; 2003-07-09; ;
grandfathered; i-ami; 'Amis; 1999-05-25; ;
grandfathered; i-bnn; Bunun; 1999-05-25; ;

# redundant
# The following codes were registered as complete tags, but can now be
# composed of registered subtags and do not require registration.

redundant; art-lojban; Lojban; 2001-11-11; ;  # use language art + variant lojban
redundant; az-Arab; Azerbaijani in Arabic script; 2003-05-30; ;  # use language az + script Arab
redundant; az-Cyrl; Azerbaijani in Cyrillic script; 2003-05-30; ;  # use language az + script Cyrl
redundant; en-boont; Boontling; 2003-02-14; ;  # use language en + variant boont

 Figure 3: Example of the Registry Format 

Maintenance of the registry requires that as new codes are assigned by ISO 639, ISO 15924, and ISO 3166, the Language Subtag Reviewer will evaluate each assignment, determine whether it conflicts with existing registry entries, and submit the information to IANA for inclusion in the registry.

The Language Subtag Reviewer MUST ensure that new subtags meet the requirements in Section 2.3Choice of Language Tag or submit an appropriate alternate subtag as described in that section. She or he will use the following form to submit this information:

LANGUAGE SUBTAG REGISTRATION FORM (NEW RECORD)
Record Text:
Type:
Subtag:
Description:
Date:
Canonical Mapping:
Recommended Prefix:
Note:

 Figure 4 

The field 'record text' contains the exact record that IANA is to insert into the Language Subtag Registry. The contents of the remaining fields must exactly match those in this field.

Whenever an entry is created or modified in the registry, the 'date' record at the start of the registry is updated to reflect the most recent modification date in ISO 8601 format.

3.2 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 and that the choice of language tag for specific content is also stable over time.

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 M49 are reflected in the IANA Language Subtag Registry. Assignments to the IANA Language Subtag Registry MUST follow the following stability rules:

3.3 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 primary language and variant subtags will be considered for independent registration. (Subtags required for stability and subtags required to keep the registry synchronized with ISO 639, ISO 15924, ISO 3166, and UN M.49 within the limits defined by this document are the only exceptions to this. See Section 3.2Stability of IANA Registry Entries.)

This procedure MAY also be used to register or alter the information for the "description", "note", or "recommended prefix" fields in a subtag's record as described in Figure 3Example of the Registry Format. Changes to all other fields in the IANA registry is NOT permitted.

If registering a new language subtag, the process starts by filling out the registration form reproduced below. Note that each response is not limited in size and should take the room necessary to adequately describe the registration.

LANGUAGE SUBTAG REGISTRATION FORM
1. Name of requester:
2. E-mail address of requester:
3. Subtag to be registered:
4. Type of Registration: 
   [ ] language
   [ ] variant
5. Description of subtag (in English or transcribed into ASCII):
6. Intended meaning of the subtag:
7. Recommended prefix(es) of subtag (for variants):
8. Native name of the language or variation (transcribed into ASCII):
9. Reference to published description of the language (book or article):
10. Any other relevant information:

 Figure 5 

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. (This is an open list. Requests to be added should be sent to <ietf-languages-request@iana.org>.)

Variant subtags are generally registered for use with a particular language range (see Section 2.4.2Matching Language Tags). For example, the subtag 'boont' is intended for use with language tags that match the language range "en", since Boontling is a dialect of English. In other words, the subtag 'boont' is intended for use in tags that start with 'en' and could include tags such as "en-Latn-boont" or "en-US-boont". This information MUST be provided in the registration form.

Any subtag MAY be incorporated into a variety of language tags, according to the rules of Section 2.1Syntax, including tags that do not match any of the intended language ranges of the registered subtag. (Note that this is probably a poor choice.) This makes validation simpler and thus more uniform across implementations, and does not require new registrations for different intended language ranges.

The intended language ranges for a given registered subtag will be maintained in the IANA registry as a guide to usage. If it is necessary to add an additional intended language range to that list for an existing language tag, that can be done by filing an additional registration form. In that form, the "Any other relevant information:" field should indicate that it is the addition of an additional intended language range.

Requests to add a language range to a subtag that imply a different semantic meaning will probably be rejected. For example, a request to add the language range "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 created for such instances.

When the two week period has passed, the subtag reviewer, who is appointed by the IESG, either forwards the request to IANA@IANA.ORG, or rejects it because of significant objections raised on the list or due to problems with constraints in this document (which should be explicitly cited). The reviewer may also extend the review period in two week increments to permit further discussion. The reviewer must indicate on the list whether the registration has been accepted, rejected, or extended following each two week period.

Note that the reviewer can raise objections on the list if he or she so desires. The important thing is that the objection must be made publicly.

The applicant is free to modify a rejected application with additional information and submit it again; this restarts the two week comment period.

Decisions made by the reviewer may be appealed to the IESG [RFC 2028]Hovey, R. and S. Bradner, The Organizations Involved in the IETF Standards Process, October 1996.[10] under the same rules as other IETF decisions [RFC 2026].

All approved registration forms are available online in the directory http://www.iana.org/numbers.html under "languages".

Updates of registrations follow the same procedure as registrations. The subtag reviewer decides whether to allow a new registrant to update a registration made by someone else; normally objections by the original registrant would carry extra weight in such a decision.

Registrations are permanent and stable. Once registered, subtags will not be removed from the registry and will remain the canonical method of referring to a specific language or variant. This provision does not apply to grandfathered tags, which may become deprecated due to registration of subtags. For example, the tag "i-navajo" is deprecated in favor of the ISO 639-1 based subtag 'nv'.

Note: The purpose of the "published description" in the registration form is intended as an aid to people trying to verify 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 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.

3.4 Extensions and Extensions Namespace

Extension subtags are those introduced by single-letter subtags other than 'x-'. They are reserved for the generation of identifiers which contain a language component, and are compatible with applications that process language tags according to this specification. For example, they might be used to define locale identifiers, which are generally based on language.

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

IANA will maintain a registry of allocated single-letter subtags. This registry contains the following information: letter identifier; name; purpose; RFC defining the subtag namespace and its use; and the name, URL, and email address of the maintaining authority.

Allocation of a single-letter subtag shall take the form of an RFC defining 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 each of the following:

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 the default fallback mechanism. For example, if the subtag 'aaa' were least significant in the tag "fr-c-aaa-bbb-ccc".



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4. Security Considerations

The only security issue that has been raised with language tags since the publication of RFC 1766, which stated that "Security issues are believed to be irrelevant to this memo", is a concern with language ranges used in content negotiation - that they may 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 you send is visible to the receiving party. 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.

Although the specification of valid subtags for an extension 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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5. 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 presentation 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 may 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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6. Changes from RFC 3066

The main goals for this revision of language tags were the following:

Compatibility. All valid RFC 3066 language tags (including those in the IANA registry) remain valid in this specification. Thus there is complete backward compatibility of this specification with existing content. In addition, this document defines language tags in such as way as to ensure future compatibility, and processors based solely on the RFC 3066 ABNF (such as those described in XML Schema version 1.0) will be able to process tags described by this document.

Stability. Because of the changes in underlying ISO standards, a valid RFC 3066 language tag may become invalid (or have its meaning change) at a later date. With so much of the world's computing infrastructure dependent on language tags, this is simply unacceptable: it invalidates content that may have an extensive shelf-life. In this specification, once a language tag is valid, it remains valid forever. Previously, there was no way to determine when two tags were equivalent. This specification provides a stable mechanism for doing so, through the use of canonical forms. These are also stable, so that implementations can depend on the use of canonical forms to assess equivalency.

Validity. The structure of language tags defined by this document makes it possible to determine if a particular tag is well-formed without regard for the actual content or "meaning" of the tag as a whole. This is important because the registry and underlying standards change over time. In addition, it must be possible to determine if a tag is valid (or not) for a given point in time in order to provide reproducible, testable results. This process must not be error-prone; otherwise even intelligent people will generate implementations that give different results. This specification provides for that by having a single data file, with specific versioning information, so that the validity of language tags at any point in time can be precisely determined (instead of interpolating values from many separate sources).

Extensibility. It is important to be able to differentiate between written forms of language -- for many implementations this is more important than distinguishing between spoken variants of a language. Languages are written in a wide variety of different scripts, so this document provides for the generative use of ISO 15924 script codes. Like the generative use of ISO language and country codes in RFC 3066, this allows combinations to be produced without resorting to the registration process. The addition of UN codes provides for the generation of language tags with regional scope, which is also required for information technology.

The recast of the registry from containing whole language tags to subtags is a key part of this. An important feature of RFC 3066 was that it allowed generative use of subtags. This allows people to meaningfully use generated tags, without the delays in registering whole tags, and the burden on the registry of having to supply all of the combinations that people may find useful.

Because of the widespread use of language tags, it is potentially disruptive to have periodic revisions of the core specification, despite demonstrated need. The extension mechanism provides for a way for independent RFCs to define extensions to language tags. These extensions have a very constrained, well-defined structure to prevent extensions from interfering with implementations of language tags defined in this document. The document also anticipates features of ISO 639-3 with the addition of the extlang subtags. The use and definition of private use tags has also been modified, to allow people to move as much information as possible out of private use tags, and into the regular structure. The goal is to dramatically reduce the need to produce a revision of this document in the future.

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

Ed Note: The following items are provided for the convenience of reviewers and will be removed from the final document.

Changes between draft-06 and this version are:



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7 References

[1] International Organization for Standardization, "ISO 639-2:1998 - Codes for the representation of names of languages -- Part 2: Alpha-3 code - edition 1", August 1988.
[2] ISO TC46/WG3 and M. Everson, Ed., "ISO 15924:2003 (E/F) - Codes for the representation of names of scripts", March 2003.
[3] International Organization for Standardization, "Code for the representation of names of languages, 1st edition", ISO Standard 639, 2002.
[4] International Organization for Standardization, "Codes for the representation of names of countries, 3rd edition", ISO Standard 3166, August 1988.
[5] Statistical 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.
[6] ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory Committee: Working principles for ISO 639 maintenance", March 2000.
[7] Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO 10021 and RFC 822", RFC 1327, May 1992.
[8] Borenstein, N. and N. Freed, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, September 1993.
[9] Alvestrand, H., "Tags for the Identification of Languages", RFC 1766, March 1995.
[10] Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process", BCP 11, RFC 2028, October 1996 (HTML, XML).
[11] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 (HTML, XML).
[12] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.
[13] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998 (HTML, XML).
[14] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998 (HTML, XML).
[15] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999 (HTML, XML).
[16] Carpenter, B., Baker, F. and M. Roberts, "Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority", RFC 2860, June 2000.
[17] Alvestrand, H., "Tags for the Identification of Languages", BCP 47, RFC 3066, January 2001.
[18] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003.


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Authors' Addresses

  Addison Phillips (editor)
  webMethods, Inc.
  432 Lakeside Drive
  Sunnyvale, CA 94088
  US
EMail:  aphillips@webmethods.com
  
  Mark Davis
  IBM
EMail:  mark.davis@us.ibm.com


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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 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 (in alphabetical order) contributed to this document or to RFCs 1766 and 3066:

Glenn Adams, Harald Tveit Alvestrand, Tim Berners-Lee, Marc Blanchet, Nathaniel Borenstein, Eric Brunner, Sean M. Burke, Jeremy Carroll, John Clews, Jim Conklin, Peter Constable, John Cowan, Mark Crispin, Dave Crocker, Martin Duerst, Michael Everson, Doug Ewell, Ned Freed, Tim Goodwin, Dirk-Willem van Gulik, Marion Gunn, Paul Hoffman, Richard Ishida, Olle Jarnefors, Kent Karlsson, John Klensin, Alain LaBonte, Eric Mader, Keith Moore, Chris Newman, Masataka Ohta, George Rhoten, Markus Scherer, Keld Jorn Simonsen, Thierry Sourbier, Otto Stolz, Tex Texin, Andrea Vine, Rhys Weatherley, Misha Wolf, Francois Yergeau 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 must go to Michael Everson, who has served as language tag reviewer for almost the complete period since the publication of RFC 1766. Special thanks to Doug Ewell, for his production of the first complete subtag registry, and his work in producing a test parser for verifying language tags.



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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 (Traditional Chinese)
en-Latn (English written in Latin script)
sr-Cyrl (Serbian written with Cyrillic script)

Language-Script-Region:

zh-Hans-CN (Simplified Chinese for the PRC)
sr-Latn-YU (Serbian, Latin script, Serbia and Montenegro)

Language-Script-Region-Variant:

en-Latn-US-boont (Boontling dialect of English)
de-Latn-CH-1996 (German written in Latin script for Switzerland using the orthography of 1996)

Language-Region:

de-DE (German for Germany)
zh-SG (Chinese for Singapore)
cs-CS (Czech for Czechoslovakia)
sr-YU (Serbian for Serbia and Montenegro)
es-419 (Spanish for Latin America and Caribbean region using the UN region code)

Other Mixtures:

en-boont (Boontling dialect of English)

private-use mechanism:

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

Extended language subtags (examples ONLY: extended languages must be defined by revision or update to this document):

zh-min
zh-min-nan-Hant-CN

Private-use subtags:

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

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. Conversion of the RFC 3066 Language Tag Registry

Upon publication of this document as a BCP, the existing IANA language tag registry must be converted into the new subtag registry. This section defines the process for performing this conversion.

The impact on the IANA maintainers of the registry of this conversion will be a small increase in the frequency of new entries. The initial set of records represents no impact on IANA, since the work to create it will be performed externally.

When this document is published, an email request will be sent from the authors of this document to the list ietf-languages@iana.org requesting the conversion of the registry. In that request, the authors of this document will provide a URL whose referred content is the proposed IANA Language Subtag Registry following conversion. There will be a Last Call period of not less than four weeks for comments and corrections to be discussed on the ietf-languages@iana.org mail list. Changes as a result of comments will not restart the Last Call period. At the end of the period, the authors will forward the URL to IANA, which will post the new registry on-line.

Tags that are currently deprecated will be maintained as grandfathered entries. The record for the grandfathered entry will contain a note indicating that the entry is 'deprecated' and reason for the deprecation.

Tags that consist entirely of subtags that are valid under this document and which have the correct form and format for tags defined by this document are superseded by this document. Such tags are placed in the 'redundant' section of the registry. For example, zh-Hant is now defined by this document.

Tags that contain subtags which are consistent with registration under the guidelines in this document will have a new subtag registration created for each eligible subtag. If all of the subtags in the original tag are fully defined by the resulting registrations or by this document, then the original tag is superseded by this document. Such tags are placed in the 'redundant' section of the registry. For example, en-boont will result in a new subtag "boont" and the RFC 3066 registered tag 'en-boont' placed in the redundant section of the registry.

Tags that contain one or more subtags that do not match the valid registration pattern and which are not otherwise defined by this document are marked as 'grandfathered' by this document.

There will be a reasonable period in which the community may comment on the proposed list entries, which SHALL be no less than four weeks in length. At the completion of this period, the Language Subtag Reviewer will notify IANA@IANA.ORG and the ietf-languages mail lists that the task is complete and forward the necessary materials to IANA for publication.

Registrations that are in process under the rules defined in RFC 3066 MAY be completed under the former rules, at the discretion of the language tag reviewer. Any new registrations submitted after the request for conversion of the registry MUST be rejected.

All existing RFC 3066 language tag registrations will be maintained in perpetuity.

The rules governing the conversion of RFC 1766 and RFC 3066 registered tags are:

Users of tags that are grandfathered should consider registering appropriate subtags in the IANA subtag registry (but are not required to).

Where two subtags have the same meaning, the priority of which to make canonical SHALL be the following:



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Intellectual Property Statement

Disclaimer of Validity

Copyright Statement

Acknowledgment