Yes, it has subtitles (which is a good thing, since GK3 has perhaps the most dialogue and the most obscure puzzles in the trilogy).
Ok, how can I enable them? because I tried and looked in the manual but I am unable to make them show up! Guess I'm gonna feel a bit silly after this question but I really tried and still no success at it lol
Always read game manual.
You enter game's settings by clicking on the right button of your mouse.
There you'll find "advanced options": turn on "captions", and it's done, subtitles are there.