Cataclysm modding require downloading 100% of the ingame content
When you play Cataclysm for the first time, you will load of elements ingame, you will see a red circle and a lot of blue shit around you :
The modding on Cataclysm, require this, all the content download, or you will get the cannot stream archive.
Language (interfaces, sounds, lua etc...) is a content, (7%), so if you change langage you have to load ingame, lot of things.
There is only 1 issue, play wow with the new langage with a normal wow.exe, and when your game reach 100% you can play with the patched exe.
For checking the %, you have to check in the ingame menu :
(Téléchargement effectué à 100%, mean my game is 100% loaded)
http://puu.sh/etrl9/857ad5fec5.jpgAnd for downloading your new langage content, you have to... wait
Also you can check the icons macros, this will force downloading icons, and it's faster than simply waiting.