We're 100% that it'll be available in Russian, English, and German. We have plans and ideas concerning other languages too, but nothing solid.
Pathologic is a very literary game, and we've been hurt by translations before. It's written in Russian. We do have a Russian-to-English translator on the team, and that's exactly why we can be sure that the English version of Pathologic won't be a lesser experience. We will be translating this game personally.
We would like the same to be true for all languages. While there definitely are many talented people out there, we're not polyglots, so it's hard for us to evaluate if something was translated well, and we're not sure we're ready to rely on freelancers. Also, ideally we would love Pathologic to be translated from Russian, not from English. We do have a non-freelance German localization team (they've translated The Void perfectly). We don't have teams for other languages yet.
Still, we do have plans and ideas. You'll be the first to know when (and if) they become solid.