Except perhaps tell me that I can use a ISO-10646-J font if I don't have a
ISO-10646-K font and
That's no exception.
I'm not sure how this fits in with the use of ISO 10646, where a language tag
It is really unfortunate that language tag draft did not predate MIME.
I assume you would want to use JIS 221, or, in China, GB13000, the Japanese
and Chinese (respectively) National Standards corresponding to ISO10646.
To do this, you will need language tags.
it's not actually a problem with Unicode,
The fatal defect of Unicode is that we can't have multi-script CJK
plain text, which we are already using.
How would you feel about a Script field instead of a language one?
We already have "charset" as mixed Script/Encoding field.