SuperTuxKart is a 3D car racing game which doesn’t cost anything as it’s another Open Source game. There are loads of racetracks, characters and other interesting things in the game.
Setting it to Gaelic is easy. Install the game (in English). The click Options » User Interface (the grey tab) » gd (Gaelic Scots). Here’s a video that shows you how to do that:
You can download it here and you will find more information about the game and project on the official SuperTuxKart website.