I would personally suggest leaving it on your main domain and creating folders for each language. Just look at what some of the major hitters are doing:

1. Amazon in French: Amazon.fr : livres, DVD, jeux video, CD, lecteurs MP3, ordinateurs, appareils photo, logiciels et plus encore !
2. Dell in Russian
3. HP in Russian

This will better allow you to focus your linking strategy on the main domain instead of having to setup a separate campaign for every new language.