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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).
2. The Language Tag
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
§ Authors' Addresses
B. Examples of Language Tags (Informative)
C. Conversion of the RFC 3066 Language Tag Registry
§ Intellectual Property and Copyright Statements
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 6.
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].
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] is:
= 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 = 5*8alphanum ; registered variants extension = singleton 1*("-" (2*8alphanum)) ; extension subtag(s) privateuse = "x" 1*("-" (1*8alphanum)) ; private use subtag(s) singleton = 1ALPHA ; 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
| Language Tag ABNF |
The character "-" is HYPHEN-MINUS (ABNF: %x2D). Whitespace in the ABNF should be disregarded. For examples of language tags, see Appendix B. Note that although [RFC 2234] 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 instance, [ISO 3166] recommends that country codes be capitalized (MN Mongolia), while [ISO 639] recommends that language codes be written in lower case (mn Mongolian). In the language tags defined by this document, however, the tag 'mn-MN' is not distinct from 'MN-mn' or 'mN-Mn' (or any other combination) and each of these variations conveys the same meaning: Mongolian for Mongolia.
For informative examples of language tags, see Appendix B at the end of this document.
The namespace of language tags and their subtags is administered by the Internet Assigned Numbers Authority (IANA)  according to the rules in Section 3 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 2.2.1.
Each subtag type has unique length and content restrictions that 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.
Note that registered subtags can only appear in specific positions in a tag. Specifically, they can only occur as primary language subtags or as variant subtags. In addition, sequences of private-use and extension subtags MUST only 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.
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. At present all languages that have both kinds of 3-character code also are assigned a 2-character code and hopefully future assignments of this nature will not arise.
Note: In order to avoid versioning difficulties in applications such as those experienced in RFC 1766, the ISO 639 Registration Authority Joint Advisory Committee (RA-JAC) has agreed on the following policy statement:
"After the publication of ISO/DIS 639-1 as an International Standard, no new 2-letter code shall be added to ISO 639-1 unless a 3-letter code is also added at the same time to ISO 639-2. In addition, no language with a 3-letter code available at the time of publication of ISO 639-1 which at that time had no 2-letter code shall be subsequently given a 2-letter code."
This will ensure that, for example, a user who implements "haw" (Hawaiian), which currently has no 2-character code, will not find his or her data invalidated by eventual addition of a 2-character code for that language."
One of the grandfathered IANA registrations is "i-enochian". The subtag "enochian" could be registered 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-min-nan' (registered under RFC 3066) might become a valid non-grandfathered tag in which the subtags 'min' and 'nan' might represent the subdialect 'nan' of the Chinese dialect 'min'.
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 written using Latin script for Switzerland.
'sr-Latn-YU' represents Serbian written using Latin script for Serbia and Montenegro (Stability rules described in Section 3.2 apply to this language tag).
'es-419' represents Spanish as spoken in the UN-defined 'Latin America and Caribbean' region.
The following rules apply to the variant subtags:
The following rules apply to extensions:
For example, if the prefix "-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".
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 C.
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 3.3.
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
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
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
The registration authority for ISO 15924 (script codes) is:
Unicode Consortium Box 391476
Mountain View, CA 94039-1476, USA
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
United Nations, Room DC2-1620
New York, NY 10017, USA
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 2.4.2 and the associated canonicalization rules contained in Section 2.4.3.
An implementation that claims to be validating MUST:
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.
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.
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.
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/1.1 :
- 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.
Implementations that are searching for content or otherwise matching language tags to a language-range [Section 2.4.1] 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:
Tag to match: en-US-boont 1. en-US-boont 2. en-US 3. en
| Default Fallback Pattern Example |
- 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 choosen, 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.
- 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.
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:
For 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.
Note: Canonicalization of language tags does not imply anything about the use of upper or lowercase letter in subtags as described in Section 2.1. 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').
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 private-use region subtags in the range AA, QM-QZ, XA-XZ and ZZ (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.
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 2434.
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.
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 3.3. 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 MUST NOT be modified: 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; de-1901; German, traditional orthography; 2001-07-17; ; grandfathered; de-1996; German, orthography of 1996; 2001-07-17; ; grandfathered; de-AT-1901; German, Austrian variant, traditional orthography; 2001-07-17; ; # 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
| 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 2.3 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:
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.
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:
- If ISO 3166 were to assign the code 'IM' to represent the value "Isle of Man" (represented in the IANA registry by the UN M49 code '833'), '833' remains the canonical subtag and 'IM' would be assigned '833' as an alias. This prevents tags that are in canonical form from becoming non-canonical.
- If the tag 'enochian' were registered as a primary language subtag and ISO 639 subsequently assigned an alpha-3 code to the same language, the new ISO 639 code would be entered into the IANA registry as a subtag with a canonical mapping to 'enochian'. The new ISO code can be used, but it is not canonical.
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 registration. (Subtags required for stability are the only exception to this. See Section 3.2.)
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 3. 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:
The subtag registration form MUST be sent to <email@example.com> 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 <firstname.lastname@example.org>.)
Variant subtags are generally registered for use with a particular language range (see Section 2.4.2). 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 registered subtag MAY be incorporated into a variety of language tags, according to the rules of Section 2.1, 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). 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] under the same rules as other IETF decisions [RFC 2026]. All registered 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.
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.
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'.
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.
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.
The issue of deciding upon the rendering of characters based on the language tag is not addressed in this memo; however, if different spans of text are not marked with font information, it may be useful to provide the ability to mark spans of text with language. For example, a rendering engine may use that information in deciding which font to use in displaying Han-based ideographs when it encounters mixed Japanese-Chinese text that has no attached font information.
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 computer implementations, this is far more important than distinguishing spoken forms. 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-04 and this version are:
|||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.|
|||ISO TC46/WG3 and M. Everson, Ed., "ISO 15924:2003 (E/F) - Codes for the representation of names of scripts", March 2003.|
|||International Organization for Standardization, "Code for the representation of names of languages, 1st edition", ISO Standard 639, 1988.|
|||International Organization for Standardization, "Codes for the representation of names of countries, 3rd edition", ISO Standard 3166, August 1988.|
|||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.|
|||Hardcastle-Kille, S., "Mapping between X.400(1988) / ISO 10021 and RFC 822", RFC 1327, May 1992.|
|||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.|
|||Alvestrand, H., "Tags for the Identification of Languages", RFC 1766, March 1995.|
|||Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process", BCP 11, RFC 2028, October 1996 (HTML, XML).|
|||Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 (HTML, XML).|
|||Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997.|
|||Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998 (HTML, XML).|
|||Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998 (HTML, XML).|
|||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).|
|||Carpenter, B., Baker, F. and M. Roberts, "Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority", RFC 2860, June 2000.|
|||Alvestrand, H., "Tags for the Identification of Languages", BCP 47, RFC 3066, January 2001.|
|||Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003.|
|Addison Phillips (editor)|
|432 Lakeside Drive|
|Sunnyvale, CA 94088|
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.
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)
- zh-Hans-CN (Simplified Chinese for the PRC)
- sr-Latn-YU (Serbian, Latin script, Serbia and Montenegro)
- en-Latn-US-boont (Boontling dialect of English)
- 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 Carribean region using the UN region code)
- en-boont (Boontling dialect of English)
Extended language subtags (examples ONLY: extended languages must be defined by revision or update to this document):
- 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):
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)
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 to the list email@example.com requesting the conversion of the registry from the authors of this document. 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 firstname.lastname@example.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 two 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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