jibz' filter wasnt working on some chinese for me, but i discovered something cool,
even though its not in the drop down list,
you can create a filter to look at the encoding language of the email, and thus catch email send in a specific character enocding.
create a filter, use header-field
and then type in the dropdown box: Content-Type
(you can see the content type of a message by doing view -> RFC-822 headers)
then choose contains, and specify the text in Content-Type you want to test for (see the headers to examine specific email content language types).
the email i was looking at said
that charset entry is specifying the encoding language
so i just used GB2312
and that gives me a filter that will catch all email sent to me in simplified chinese.