The only info about the amount of text in the game we have is this:
Dawn of Fantasy brings innovation and show- manship to the single player campaign, delivering intensely scripted 30 hours of non-linear narratives, filled with 600 minutes of dialogues, developed by a team of 12 acclaimed designers and writers.
It seams like a lot of work that should be done by a team of people rather than just one person unless one would wish to disregard single player elements and only translate those pieces of text related to gameplay, interface etc. Of course the dialogues might contain acted voice overs which would look weird with a translation in another language.
But I have no idea how would this be implemented (what files need to be edited etc.) but if you're serious about translating the game into Polish maybe one of the devs. would be willing to help you with the technical issues. In one of the earlier threads there was mention of a group of people who translate games into Italian so this sort of thing is not unheard of.
The game's "mother tongue" is English as is usually the case.
Don't forget you've got "The Witcher", an awesome Polish game. I'm still waiting for that extended version with the fixed English translations and dialogues.