Thanks for your reply :-)

I've heard that Emacs 22 already supports utf8 Chinese encoding. I've
tried the CVS version of Emacs 22(because Emacs 22 in Gentoo is still
masked), but the result is the same. And if I use Emacs 22 then I will
have to reinstall all the add-on since they are compiled by Emacs 23.

And I am wondering why it works fine before the recompilation even
without any configuration about Chinese, but after that I can't get it
work as well as before.