Is there any way to change the language of the game? I am talking about subs, not audio.
You mean on the fly? No, I don't think this is currently supported.
For the fan translated
version (English), there is a way to revert back to the Polish version without reinstalling the game. But it would require editing the prince.ini file to add a section for the polish version and then creating a different shortcut to launch the Polish version of the game.
In that case you'll get differently named save game files per version, but if you rename them to match the other language, the save games should be compatible and appear on your loading screen.