You can use any WoW client you want, English, German, Spanish, whatever. However you have to modify a file or two, really easy though only takes 2 mins.
If you want to be able to read the Chinese text instead of seeing a bunch of ?????? whenever someone uses Chinese, you have to find and download the Chinese fonts that come with the Chinese version of WoW. Everything else works just great.
I can give you a hand when you need to set stuff up.
I'm in a guild that is getting quite large. We use only English in guild chat. Lots of people of all levels. We're in Region 1 (shanghai), on the 山丘之王 (<-- you won't be able to read that unless you get the fonts) server. Guild name is "the foreigners".
Shanghai and Guangdong share the same payment option thingy, so you can come try your latency on our server if you want. If its too high you can create a character on a Guangdong server without having to make a new account.
Let me know if you need some help.