rfc1766.txt

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Network Working Group                                      H. Alvestrand
Request for Comments: 1766                                       UNINETT
Category: Standards Track                                     March 1995


                Tags for the Identification of Languages

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document describes a language tag for use in cases where it is
   desired to indicate the language used in an information object.

   It also defines a Content-language: header, for use in the case where
   one desires to indicate the language of something that has RFC-822-
   like headers, like MIME body parts or Web documents, and a new
   parameter to the Multipart/Alternative type, to aid in the usage of
   the Content-Language: header.

1.  Introduction

   There are a number of languages spoken by human beings in this world.

   A great number of these people would prefer to have information
   presented in a language that they understand.

   In some contexts, it is possible to have information in more than one
   language, or it might be possible to provide tools for assisting in
   the understanding of a language (like dictionaries).

   A prerequisite for any such function is a means of labelling the
   information content with an identifier for the language in which is
   is written.

   In the tradition of solving only problems that we think we
   understand, this document specifies an identifier mechanism, and one
   possible use for it.







Alvestrand                                                      [Page 1]


RFC 1766                      Language Tag                    March 1995


2.  The Language tag

   The language tag is composed of 1 or more parts: A primary language
   tag and a (possibly empty) series of subtags.

   The syntax of this tag in RFC-822 EBNF is:

    Language-Tag = Primary-tag *( "-" Subtag )
    Primary-tag = 1*8ALPHA
    Subtag = 1*8ALPHA

   Whitespace is not allowed within the tag.

   All tags are to be treated as case insensitive; there exist
   conventions for capitalization of some of them, but these should not
   be taken to carry meaning.

   The namespace of language tags is administered by the IANA according
   to the rules in section 5 of this document.

   The following registrations are predefined:

   In the primary language tag:

    -    All 2-letter tags are interpreted according to ISO standard
         639, "Code for the representation of names of languages" [ISO
         639].

    -    The value "i" is reserved for IANA-defined registrations

    -    The value "x" is reserved for private use. Subtags of "x"
         will not be registered by the IANA.

    -    Other values cannot be assigned except by updating this
         standard.

   The reason for reserving all other tags is to be open towards new
   revisions of ISO 639; the use of "i" and "x" is the minimum we can do
   here to be able to extend the mechanism to meet our requirements.

   In the first subtag:

    -    All 2-letter codes are interpreted as ISO 3166 alpha-2
         country codes denoting the area in which the language is
         used.

    -    Codes of 3 to 8 letters may be registered with the IANA by
         anyone who feels a need for it, according to the rules in



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RFC 1766                      Language Tag                    March 1995


         chapter 5 of this document.

   The information in the subtag may for instance be:

    -    Country identification, such as en-US (this usage is
         described in ISO 639)

    -    Dialect or variant information, such as no-nynorsk or en-
         cockney

    -    Languages not listed in ISO 639 that are not variants of
         any listed language, which can be registered with the i-
         prefix, such as i-cherokee

    -    Script variations, such as az-arabic and az-cyrillic

   In the second and subsequent subtag, any value can be registered.

   NOTE: The ISO 639/ISO 3166 convention is that language names are
   written in lower case, while country codes are written in upper case.
   This convention is recommended, but not enforced; the tags are case
   insensitive.

   NOTE: ISO 639 defines a registration authority for additions to and
   changes in the list of languages in ISO 639. This authority is:

         International Information Centre for Terminology (Infoterm)
         P.O. Box 130
         A-1021 Wien
         Austria
         Phone: [phone] Ext. 312
         Fax:   [phone]

   The following codes have been added in 1989 (nothing later): ug
   (Uigur), iu (Inuktitut, also called Eskimo), za (Zhuang), he (Hebrew,
   replacing iw), yi (Yiddish, replacing ji), and id (Indonesian,
   replacing in).

   NOTE: The registration agency for ISO 3166 (country codes) is:

         ISO 3166 Maintenance Agency Secretariat
         c/o DIN Deutches Institut fuer Normung
         Burggrafenstrasse 6
         Postfach 1107
         D-10787 Berlin
         Germany
         Phone: [phone]
         Fax:   [phone]



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RFC 1766                      Language Tag                    March 1995


   The country codes AA, QM-QZ, XA-XZ and ZZ are reserved by ISO 3166 as
   user-assigned codes.

2.1.  Meaning of the language tag

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

   There is no guaranteed relationship between languages whose tags
   start out with the same series of subtags; especially, they are NOT
   guraranteed to be mutually comprehensible, although this will
   sometimes be the case.

   Applications should always treat language tags as a single token; the
   division into main tag and subtags is an administrative mechanism,
   not a navigation aid.

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

    -    For a single information object, it should be taken as the
         set of languages that is required for a complete
         comprehension of the complete object. Example: Simple text.

    -    For an aggregation of information objects, it should be taken
         as the set of languages used inside components of that
         aggregation.  Examples: Document stores and libraries.

    -    For information objects whose purpose in life is providing
         alternatives, it should be regarded as a hint that the
         material inside is provided in several languages, and that
         one has to inspect each of the alternatives in order to find
         its language or languages.  In this case, multiple languages
         need not mean that one needs to be multilingual to get
         complete understanding of the document. Example: MIME
         multipart/alternative.

    -    It would be possible to define (for instance) an SGML DTD
         that defines a <LANG xx> tag for indicating that following or
         contained text is written in this language, such that one
         could write "<LANG FR>C'est la vie</LANG>"; the Norwegian-
         speaking user could then access a French-Norwegian dictionary
         to find out what the quote meant.






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RFC 1766                      Language Tag                    March 1995


3.  The Content-language header

   The Language header is intended for use in the case where one desires
   to indicate the language(s) of something that has RFC-822-like
   headers, like MIME body parts or Web documents.

   The RFC-822 EBNF of the Language header is:

    Language-Header = "Content-Language" ":" 1#Language-tag

   Note that the Language-Header is allowed to list several languages in
   a comma-separated list.

   Whitespace is allowed, which means also that one can place
   parenthesized comments anywhere in the language sequence.

3.1.  Examples of Content-language values

   NOTE: NONE of the subtags shown in this document have actually been
   assigned; they are used for illustration purposes only.

   Norwegian official document, with parallel text in both official
   versions of Norwegian. (Both versions are readable by all
   Norwegians).

      Content-Type: multipart/alternative;
             differences=content-language
      Content-Language: no-nynorsk, no-bokmaal