Just making this post to let the Linux users know, if you cannot see any text when starting a game (when you name your kingdom), it is working fine. It will use what you type. Apparently it's due to the font being missing(?), but rest assured if you type the name in correctly, it will show. I only own the GOG version and this did work for me.

Fix help: Steam forums.

Official developer reply:
Just following up on this: A user on our game forum has pointed out that the keyboard is actually working, it's just not displaying the text properly (presumably due to a missing font). So if you type your Kingdom's name in carefully and hit Enter, it should all work fine.

Sorry about that.

Source: http://steamcommunity.com/app/226620/discussions/0/540744936389357015/