This was discussed in the work with the Language Tag for MIME
etc. I mentioned (draft-ietf-mailext-lang-tag-00.txt). This
was the result (and I quote):
    1.  The Language tag
    The language tag is composed of 2 parts: A language tag and a
    subtag.
    The syntax of this header is:
    Language-Header ::= 'Content-language:' Language [',' Language]...
    Language ::= ALPHA*8 [ '-' ALPHA*8 ]
    The namespace of language tags and subtags is administered by the
    IANA. The following registrations are predefined:
    In the language tag:
    -    All 2-letter codes are interpreted according to ISO 639.
    -    All 3-letter codes are reserved for the (hopefully)
         forthcoming revision to ISO 639
    -    The value "IANA" is reserved for IANA-defined
         subregistrations
    -    The value "X" is reserved for private use. Subtags of "X"
         will not be registered by the IANA.
    -    No other registration is allowed.
    In the sublanguage tag:
    -    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 sublanguage tag may for instance be:
    -    Country identification, such as en-US (this usage is
         described in ISO 639)
    -    Dialect information, such as no-NYNORSK or en-COCKNEY
    -    Languages not listed in ISO 639, which can be registered with
         the IANA prefix, such as IANA-CHEROKEE
    If multiple languages are used in the MIME body part, they are
    listed with commas between them.
And, later
    3.  Usage examples
    Examples of protocol usage of this header are:
    -    WWW selection of an appropriate version of information for
         display, based on a profile for the user listing languages
         that are understood
    -    MIME usage of alternate body parts in E-mail
So, *this* part of the work is already done, just to use.
--- Peter Svanberg Email: psv@nada.kth.se Dept of Num An & CS, Royal Inst of Tech Phone: +46 8 790 71 40 S-100 44 Stockholm, SWEDEN Fax: +46 8 790 09 30