You can use ActiveCollab in Czech, Dutch, French, German, Italian, Polish, Portuguese, Swedish, Spanish, Turkish, Hungarian, Croatian, Serbian and Russian.
Changing language is easy. Once you’re in ActiveCollab, click on your name in the lower left corner and then Profile. There you set your personal preference for the language.
Want to change language for all new users, so when you invite someone, they can start using ActiveCollab right away in their native language? You can do that in System Settings > General Settings.