yeah it is strange in a future space adventure to see any concrete nationality to the character, I mean most of them are divided up from their factions. That came from one big colonization of humans that classically as humans are tend to split politically. In Konstantin's case considering he is mostly robotic, his voice could just have came from something his brain was downloaded to. So his factory setting could just be that he got a russian voice. I don't know.
I think there is a lot that goes on in the background that we don't see in-game. For instance Ayana is said to work for hades, because in return hades faction pays her big bucks that she in turn give back to her hometown, a mining community. If we think about this, that means there's some form of society that has some kind of everyday life. If we go back to the archives and read about the first group of humans that came to the broken planet. They are a corporation that kept their findings a secret and was whisked away to deep space. If we then think about a corporation type society often a corporation (specially a technological based one) we could get diversity from all kinds of places around the world. They would hire all kinds of people that are the best of the best in their field of work, regardless of where they are born. That could be the root of where all the different nationality voices stem from. So imagine the first colony of people that were whisked to the broken planet a sort of mayflower if you will....
Or IDK maybe the voice actors were like lol this guy looks like he would rock a russian voice, Ima give him a russian accent. boom. Konstantin lives for mother fith council.