I would say that for japanese, you should restrict the email
address to ascii, or you'll have trouble. The user's name
however should allow kanji. In japanese you also need to
add a field to the user info which contains the pronunciation (in
kana) of the user's name, since the kanji are ambigious and
also people sometimes don't know the obscure ones.
I have a note about how to convert half-wifdth kana to full width,
using a tcl routine. Sometimes people enter the pronunciation in
half width (aging Microsoft charset) and it screws up the
sort order unless you canonicalize it to full width kana.
