
draft                        Language Tag                    August 94


                 Tags for the identification of languages

                     Fri Aug  5 14:21:43 MET DST 1994


                         Harald Tveit Alvestrand
                                 UNINETT
                      Harald.T.Alvestrand@uninett.no






    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.


    Status of this Memo

    This draft document is being circulated for comment.

    If consensus is reached it may be submitted to the RFC editor as a
    Proposed Standard protocol specificiation.

    Please send comments to the author, or to the MAILEXT mailing list
    <mailext@cs.wisc.edu>

    The following text is required by the Internet-draft rules:

    This document is an Internet Draft.  Internet Drafts are working
    documents of the Internet Engineering Task Force (IETF), its
    Areas, and its Working Groups. Note that other groups may also
    distribute working documents as Internet Drafts.

    Internet Drafts are draft documents valid for a maximum of six





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    months. Internet Drafts may be updated, replaced, or obsoleted by
    other documents at any time.  It is not appropriate to use
    Internet Drafts as reference material or to cite them other than
    as a "working draft" or "work in progress."

    Please check the I-D abstract listing contained in each Internet
    Draft directory to learn the current status of this or any other
    Internet Draft.

    The filename of this document is draft-mailext-lang-tag-01.txt







































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    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 dicationaries).

    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.


    2.  The Language tag

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

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


    Language-Tag = Tag-List
    Tag-List = Tag-Component *[ '-', Tag-List ]
    Tag-Component = 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 and subtags is administered by the
    IANA. The following registrations are predefined:

    In the language tag:






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    -    All 2-letter codes are interpreted according to 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 country codes,
         according to the rules laid down in ISO 639.

    -    Codes of 3 to 8 letters may be registered with the IANA by
         anyone who feels a need for it. IANA has the right to reject
         registrations that are felt to be misleading.

    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.






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    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: +43 1  26 75 35 Ext. 312
         Fax:   +43 1 216 32 72

    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 Für Normung
    Burggrafenstrasse 6
    Postfach 1107
    D-10787 Berlin
    Germany
    Phone: +49 30 26 01 320
    Fax:   +49 30 26 01 231

    The 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 that start





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    out with the same series of tags; 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 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.


    3.  The Content-language header

    The RFC-822 ABNF of the Language header is:

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





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    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

    Voice recording from the London docks

      Content-type: audio/basic
      Content-Language: en-cockney

    Document in Sami, which does not have an ISO 639 code, and is
    spoken in several countries, but with about half the speakers in
    Norway, with six different, mutually incomprehensible dialects:

      Content-type: text/plain; charset=iso-8859-10
      Content-Language: i-sami-no (North Sami)

    An English-French dictionary

      Content-type: application/dictionary
      Content-Language: en, fr (This is a dictionary)

    An official EC document (in a few of its official languages)

      Content-type: multipart/alternative
      Content-Language: en, fr, de, da, el, it

    An excerpt from Star Trek






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      Content-type: video/mpeg
      Content-Language: x-klingon


    4.  Use of Content-Language with Multipart/Alternative

    When using the Multipart/Alternative body part of MIME, it is
    possible to have the body parts giving the same information
    content in different languages. In this case, one should put a
    Content-Language header on each of the body parts, and a summary
    Content-Language header onto the Multipart/Alternative itself.


    4.1.  The differences parameter to multipart/alternative

    As defined in RFC 1541, Multipart/Alternative only has one
    parameter: boundary.

    The common usage of Multipart/Alternative is to have more than one
    format of the same message (f.ex. PostScript and ASCII).

    The use of language tags to differentiate between different
    alternatives will certainly not lead all MIME UAs to present the
    most sensible body part as default.

    Therefore, a new parameter is defined, to allow the configuration
    of MIME readers to handle language differences in a sensible
    manner.

    Name: Differences
    Value: One or more of
         Content-Type
         Content-Language

    Further values can be registered with IANA; it must be the name of
    a header for which a definition exists in a published document.
    If not present, Differences=Content-Type is assumed.

    The intent is that the MIME reader can look at these headers of
    the message component to do an intelligent choice of what to
    present to the user, based on knowledge about the user preferences
    and capabilities.

    (The intent of having registration with IANA of the fields used in





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    this context is to maintain a list of usages that a mail UA may
    expect to see, not to reject usages)

    (NOTE: The MIME specification [RFC 1521], section 7.2, states that
    headers not beginning with "Content-" are generally to be ignored
    in body parts. People defining a header for use with
    "differences=" should take note of this)

    The mechanism for deciding which body part to present is outside
    the scope of this document.

    MIME EXAMPLE:

    Content-Type: multipart/alternative; differences=Content-Language;
              boundary="limit"
    Content-Language: en, fr, de

    --limit
    Content-Language: fr

    Le renard brun et agile saute par dessus le chien paresseux
    --limit
    Content-Language: de
    Content-Type: text/plain; charset=iso-8859-1
    Content-Transfer-encoding: 8bit

    Der schnelle braune Fuchs hüpft über den faulen Hund
    --limit
    Content-Language: en

    The quick brown fox jumps over the lazy dog
    --limit--

    When composing a message, the choice of sequence may be somewhat
    arbitary. However, non-MIME mail readers will show the first body
    part first, meaning that this should most likely be the language
    understood by most of the recipients.


    5.  IANA registration procedure for language tags

    Any language tag must start with an existing tag, and extend it.







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    This registration form should be used by anyone who wants to use a
    language tag not defined by ISO or IANA.

    ----------------------------------------------------------------------
    LANGUAGE TAG REGISTRATION FORM

    Name of requester          :
    E-mail address of requester:
    Tag to be registered       :

    English name of language   :

    Native name of language (in ASCII):

    Reference to published description of the language (book or article):
    ----------------------------------------------------------------------
    The language form must be sent to language-review@uninett.no for a
    2-week review period before submitting it to IANA.  (This is an
    open list. Requests to be added should be sent to language-review-
    request@uninett.no. General language discussions are not
    appropriate for this list)

    The completed form should then be sent to IANA@ISI.EDU; all
    registered forms are available online in the directory
    ftp://ftp.iana.isi.edu/registrations/languages/

    (NOTE: The IANA may suggest alternative text here).

    The IANA is free to reject registrations where it feels, based on
    list feedback, that information is lacking, or that the tag name
    suggests something different from the language referenced.


    6.  Security considerations

    Security considerations are not considered in this memo


    7.  Character set considerations

    Codes are always expressed using US-ASCII (a-z).

    The issue of deciding upon the rendering of a character set based
    on the language encoding is not addressed in this memo; however,





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    the author cautions against thinking that such a decision can be
    made correctly for all cases unless means of switching language in
    the middle of a text are defined (for example, a rendering engine
    that decides font based on Japanese or Chinese language will fail
    to work when a mixed Japanese-Chinese text is encountered)


    8.  Gatewaying considerations

    RFC 1327 defines a Language: header. This header is not
    recommended now, because it is defined to be a single 2-letter
    language code, and the X.400 header it is supposed to gateway is a
    list of language codes.

    It is suggested that RFC 1327 be updated to produce the Content-
    Language: header, and to turn this header into the ISO/CCITT
    specified Language components rather than the RFC-822-headers
    heading extension.


    9.  References


    [ISO 639]
          ISO 639:1988 (E/F) - Code for the representation of names of
         languages - The International Organization for
         Standardization, 1st edition, 1988 17 pages Prepared by
         ISO/TC 37 - Terminology (principles and coordination)


    [ISO 3166]
         ISO 3166:1988 (E/F) - Codes for the representation of names
         of countries - The International Organization for
         Standardization, 3rd edition, 1988-08-15


    [RFC 1521]
         MIME Part One: Mechanisms for Specifying and Describing the
         Format of Internet Message Bodies - Borenstein and Freed -
         September 1993


    [RFC 1327]
         Mapping between X.400(1988) / ISO 10021 and RFC 822 - Kille -





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         May 1992


    10.  Change log   Changes from draft-ietf-lang-tag-02.txt:

         Clarified that a language tag is a single token

    Changes from draft-alvestrand-language-tag-00:

         IANA registration form added

         IANA-reserved tag changed from "IANA" to "I", in order to
         avoid clashing with possible ISO 4-letter codes

         Separated "tag" definition from "header" definition

         Info on ISO 639 registration office added

         Created a multi-level tag, rather than strict two-level

         Added examples of SGML usage

         Lots of small nits fixed


























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