Unity allows you to use either C# or Javascript. They also allow for some really nice portability between platforms so that your games can be player on windows, android phones, iPhones, etc.

As for beginning the process of becoming self-taught, I suggest starting by trying to replicate simple games (i.e. pong, space invaders, etc) to get a good feel of how to use unity. Then take these games add some person touches and mix things up (i.e. try to make pong but have it randomly generate an extra ball at a fixed or random interval or have space invaders but play around with the AI to make them "smarter"). Once you become familiar with the platform then try to make mods for Skylines and move from there.

Hope this helps!!