First of all, the options that are grayed out are only available for change out of game, so in the main menu. That means that if you want to change that Russian into something else, you need to go to the main menu and click the gear icon on the top. Secondly, the tower is in Russian because you are in a Russian Airforce aircraft on the Russian side of the map. As of yet there is no way to change that language without some advanced knowledge of the ME (e.g. open the missions from the campaign individually in the Mission Editor and change the coalition/country to NATO). The back seater is supposed to be in English as is the briefing. In my experience, the (Russian) ATC is not needed for this campaign. Sure, it adds a little immersion, but you will be totally fine when you do not use it. You will not fail any mission etc. You can even check your kneeboard and see which runway is in use and what way you are supposed to taxi etc. Hope this helped you out a bit!