Just as a short explanation why the subject won't work with simple UTF-8 encoding: The subject line is transmitted in the header, and all headers need to be ASCII.

This is because mail server mostly care only about the headers, and keeping them in clean ASCII removes the woes of the MTA authors to handle multiple encodings (and multi byte encodings).

P.S. For some reason the utf-8/Chinese characters get changed when you copy paste them to VI. If you have this problem you can first copy the chars to a notepad and then to VI.

Maybe your vi(m) isn't configured properly? You can use :set encoding=utf8 to fore the use of utf-8, and the option fileencoding can controls the encoding in which the file is stored to disk. If these options are different, vim converts between them automatically.

So far I had only problems with vim when a file had mixed charsets (like latin1 + utf8).