Was a little disappointed that chinese subtitles don’t work out-the-box on mplayer. Well, ass ones seem to work fine, but srt ones don’t work at all and I had to Google it. Anyway, assuming you already have fonts that can display chinese characters, you can get mplayer to play chinese subs by giving it the parameter
mplayer -subcp cp936 your.moviefile
-subcp enca:zh:BIG5 also works, and seems to work better in some cases:
mplayer -subcp enca:zh:BIG5 your.moviefile
(thanks to Kees in the comments)
You can also use the -font option to manually specify a font that mplayer should use. Source.