Depends on where you got your Slide. During my time with Nokia, phones of the same model, but going to different regions around the world, will get different regional software. Here in the USA, only English and Spanish were loaded. You would have to get a regional set of software installed.
Being in China, I imagine there are many specialized shops that are able to do this, provided the Slide is available in China... If you are a T-Mobile customer traveling in China, I'd start by calling them, they may be able to send you an OTA update for the regional languages.
Edit: Also, try searching the Market for language packs. I have no idea if this is even possible, but worth a shot. You could also try manually adding a hotspot.
: T-Mobile Samsung Galaxy S3 (SGH-T999)
: Official stock JB from T-Mobile
: Acer Iconia A500
: CM10 Jelly Bean 4.1
: Thor's 1.7 Touch Recovery of CWM
If I do not Thank your thread, it's because of the XDA Classic forum theme, sorry...