If you still have a clean copy of en 2.4x, here is what to do.
1.keep a copy of the chinese 3.05 wow.exe elsewhere (for later use)
2.replace the installation with your clean copy of 2.4x (while, keep the /wtf and /interface if you want, these folders store your personal settings and addons)
3.update using the 2.4x launcher which will iniate download patch of 3.03
4.when you ve done and up to 3.03, replace the exe with your chinese 3.05 wow.exe
5.you are ready to enjoy an english client on the chinese server.