Thanks a lot, I'm glad you like my game this much, as for the languages I currently only plan two: my own (Polish) and English which is universally used.
The voices are going to stay the same because there is a story reasons behind those (some characters natively speak Polish because the game takes place there and foreigners speak English, this is just for better immersion)
At some point after release of the game, I'll be adding various other languages to the game when I earn enough funds for it and I'll have more time of course.
It can be a bit difficult to make a proper file system for it, but I'm sure I can figure something out some day. In any case I'll try to keep text files open for modding if anyone wanted to translate it by themselves