I do believe the Official firmware supports Several Languages. so please re-flash the firware or do Factory Reset. Upon boot it will prompt to choose language.
If the official firmware does not support Polish then you will have to check the Custom Roms to see if they do.
The T999V has a lot of available languages. I might have a rom from a while back built from that firmware. Ill check, but it wont be totally up to date.
Heres a link to the T999V rom if you want to try it. Its built from LH2 though, which is 4.1.2 I think. I dont know for sure if it has Polish, I just know it had a lot more than the T999 roms. Hope it helps.
First thing to try is to take the cameradata folder from a T999 rom and copy it over yours (back up the original first). Doesn't always work but is one of the easier steps to start with.