Compatibility between servers

Hello, I would like to learn some new languages like French, Italian, Deutsch and Russian while playing WoW

For that, I would like to ask the next:

If I donwload the WOTLK new version with Legion models from Warmame, and I switch the realmlist to (for example) a native french private server, it will work or it will have compatiblity problems due to the different character customizations?

Or should be better to download the WOTLK normal old version?

And, how I can do to download WoW in those different languages? Thanks!