To edit text, use SA2CutsceneTextEditor and SA2MEssageTextEditor which come with SATools. Text files are located in the MessageK and Message for in-game text like hints in Knuckles/Rouge stages, interacting with mystic melody statues, etc. Cutscene text files are located in the event folder in the gd_PC folder. From there (assuming you'll be converting from English to Polish) you'll want to use evmesH1.prs for the hero cutscenes, evmesD1.prs for dark cutscenes, and evmesL1.prs for Last Story cutscenes.
if you want to change the cutscene text. you must use the cutscene text editor and you have to use one of the already available languages. i suggest using the english dialouge first and translating that, then saving it using the name for another language so that english is still and option.