Can I do that?

Can I rename the ingame items, addons, perks etc? I want to translate the game to my language.

Thats a good idea, I want to know this aswell. / Szivesen segítenék amennyiben lehetséges ez a történet. :-)

Since you want to spend the time translating it youre probably better off asking the devs of the game if they will do it and you will help to translate the text. That way it is safer and works everytime the game is updated and it aids everyone in your country. They just added polish to the game so you probably have a good chance of them listening to you.