Game is half English and half Russian

If I go to Rewards section some of the rewards are in Russian.
When I try to play a Skirmish I select the Russian Faction (in Russian) and it goes back to American Faction.

It's probably because you're playing with the New Steam version. As of right now, this mod isn't compatible with that version but the devs are working to fix it. It should come out in a couple of weeks.