Regarding the Filename parameter, none of Asia language is taken into
consideration. As result, it is sort of nightmare in specially Japan.
Many copmanies use different encoding scheme. This is because none of
RFC does allow to use Asia character for file name as of today, it
allows only US-ASCII.
I believe this is solved with draft-moore-mime-cdisp-01.txt, which
references draft-freed-pvcsc-03.txt.
In particular, a content-disposition header could look like
content-disposition: attachment; filename*=iso-2022-jp'xx'yyyyyyyy
where xx is the ISO 639 language code for Japanese (sorry, I don't
have a copy of ISO 639) and yyyyyyyy is Japenese text in iso-2022-jp
charset encoded using URL-style "%XX" encoding for each octet.
Unfortunately, the encoding is very inefficient. Each Japanese
two-octet character will require six ASCII characters to encode (for
example, ABCD hex gets encoded as "%AB%CD") Text in the UTF-8 charset
would require even more encoding overhead using this method.
So while it is possible to encode text in any language using this
method, I could certainly understand if users of Asian languages would
prefer a more efficient encoding for those languages.
Keith