you can copy the localisation files of a english client into your chinese wow. But either way you'll need both client to have the files, and have them updated when needed.
The easiest way is to get the client in the language you want (can find it on www.wowwiki.com/Patch_mirrors or download the client installer on the official wow EU/US website) and do it the way explained on the guide.
When you log on a realm type "/join english
" to get in touch with the community members.
WoW English/Chinese glossary
(2000+ translated words) found on wow-in-chinese.jfs-web.chEnglish speakers are consolidating on the same realm for Cataclysm check this thread