XBMP 2-11 CVS release support Traditional Chinese now!!!!
I made it work on my xbox.
1. Get the latest CVS build from xbins ftp.
2. edit the config.xml to fit your system. remenber to edit 3 items for the use of chinese
set "subtitleencoding" to your language's encoding "big5" for chinese
set "usettfuifont" to true (only TTF fonts can display multibyte characters)
set "language" to your language code. : 42 for chinese.
3. After editing the config.xml. please get into locale directory and copy lang-8.xml to lang-42.xml. and open the lang-1.xml, copy the last item regarding to "IMDB" and paste this item to lang-42.xml.
4. get the TTF font file from your windows system and copy it to the media directory of xbmp. I use kai.ttf. rename it as "common-font.ttf".

that's all, enjoy a full chinese support of GUI/subtitle.