Your website can be in any language you choose. All the training here at WA is in English but that should not deter you from using any language in which you are fluent on your own website. Your posts and questions at WA need to be in English as that's the only language supported. ~Marion

Hi, yes you can, then use a translation service to translate it into any language you wish. There are many free translation services on the net, just Google what, I imagine, in your case, would be Chinese to English (US).
How accurate these free translation services are, or how many words they allow I don't know, Ive never used them and they may charge for a more professional service. If you do use a translation service you may wish to copy the translation and PM me and I'll have a look and correct any any typos or grammatical errors it may contain, if any. Hope this helps.

I guess you can providing your targeted audience will read it, and that all your keywords are in the same language.

All the training and support is in English, but if you are fluent in more than one language you should be able to use the training in any language. Just don't expect much help for your website if there are problems because WA only supports the English language.

I don't see why not. If your niche is aimed for your conrty then i would say go for it. Hope this has helped?