ANOTHER FIX IS AVAILABLE WHICH TRANSLATE THE GAME AT 100% http://wow-in-chinese.forum2jeux.com/t2122-cataclysm-4114250-fix-final-guide#19778
Ok so first of all all credits goes to the guys who made the tests and posted vital infos on the brainstorming thread, particularly ublack who provided a lot of informations and kind of saved the day.
I'm reposting the guide he wrote for the sake of visibility.
By using this almost everything is translated except for the items names (for now but you can the delocalize addon to get some translations).
1 - Install the enUS client (https://us.battle.net/account/downloads/WoW-4.0.0-Trial-enUS-Installer.exe) and let it fully update until it says Wow is up to date. (Critical updates must be finished also, so your cache files are 100% built)
2 - Download the chinese root files and extract it whenever you want (dont extract into your enUS installation you're probably going to need that install when the next update is released)
Reuploaded Chinese root files, You can rename the folder from World of Warcraft to whatever you want:
3 - Copy the Data folder from the enUS client to the folder that has the Chinese root files.
4 - Delete the 14333 files in the Data, enUS and Data\Cache folders.
5 - Rename the Data\enUS and the files within this folder from enUS to enCN
6 - Download this file, save in the enCN folder and rename to wow-update-enCN-13623.MPQ
(Dont modify this file, the game won't accept the file if you modify it. If you did you have to download it again or maybe repack the file)
7 - Copy the Chinese realmlist over to the enCN folder.
8 - Open the wow.mfil with notepad delete everything that's in it, save the file and make it read-only.
9 - Change to or add SET locale "enCN" to the WTF\config.wtf file
10 - Download both wow-update-base-14250.MPQ and wow-update-enCN-14250.MPQ or create them yourself (the enCN file needs to have the db2 files extracted from the chinese locale-enCN)
11 - Get either skeleton
(edit Skeleton.ini, use skipsignature=1)
or the fixed .exe to launch the game.
That's it I think, you're going to have a full enUS client except for items names but you can use an addon for that. Now I'm trying to figure out how to make the game accept the enUS db2 files, but maybe someone should ask the guy who developed skeleton or the one that did the fixed exe if they can do something about it.
It's not practical having to copy the Data\Cache folder from the enUS client but it needs to be done.
Feel free to make any changes to this 'guide' and repost anywhere you want. You can also upload your own version of the files so people know they can trust it 100%.