(A decent
mail composing agent could of course be configured to attach the
user's native language by default to all outgoing messages.)
Yes. I myself would configure such a program so that the default
would be *not* to attach language info, since I sometimes write in
English, sometimes in Japanese, and sometimes in both. I might use
the language tags occasionally, maybe in multipart/alternative.
To mention one example, if a message is marked as being in
German, and uses a charset which contains umlauted characters
and the German double-s character, a display process at the
recipient's end which did not have those characters available
could transliterate them:
<ss> => ss
<a-diaeresis> => ae
<o-diaeresis> => oe
etc.
If the language is known to be German, these transliterations
are appropriate, and highly recommended. However, for other
languages (or if the language is not known), they are not
appropriate.
Hmmm... Interesting. Here again we have the "the way the sender sees
it, and the way the receiver wants to see it" dichotomy. For example,
the Japanese name 九州 is sometimes transliterated as Kyushu (when the
reader is expected to be an English-speaker), but I have also seen it
transliterated as Kjoesjoe when the audience is expected to be Dutch.
Then again, the character 字 is transliterated into several different
forms in English, depending on the language it was written in (zi, ji,
and ja for Chinese, Japanese and Korean respectively). So, yes,
language tags would be useful here, but the "correct" transliteration
would depend on the receiver's language!
Regards,
Erik