Here is the version I promised to send out after the IETF.
It contains a change log, so you can see what changed.
Note: it is now in the "mailext" working group, rather than being
a private contribution.
Note that some information inside it required the use of ISO 8859-1,
thus, it is encoded as Quoted-Printable!
(Those of you with MIME mail readers should not notice)
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,
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)
Wow! You still think "Content-language:" may have something to do with
charset?
Manyou Gana is a system to transcribe pronounciation with Japanese
Han characters. It can represent English text.
So, what can you do with single-lingual text
Content-language: en
charset=brain-dead-CJK-unified
represented in Manyou Gana?
The section should be:
7. Character set considerations
Codes are always expressed using US-ASCII (a-z).
The issue of deciding upon the rendering of a character set is
controled only by charset paramter in Content-type header and
has nothing to do with the language tag.
Masataka Ohta