How can i translate the game by myself?

[Radmir Rope]

Can i just open and edit the file?If yes which one?

[Mistic]

If you want information and instructions about how to translate the game, take a look at the Translation Project:
http://steamcommunity.com/groups/analoguetts

[Beridok]

Unpack .RPA files, then edit .RPY files with something like Notepad++