OpenTTD is a virtual world based on Transport Tycoon Deluxe. Your task is to set up a network of buses, trains, planes and ships. You can play it in single player mode, or against other people as a network game or online.
You have to install it first (the installation file is here). You can then set it to Gaelic by going to Game Options » Language » Scottish Gaelic:
You can get detailed a game guide here (in Gaelic) and on the general project wiki.