I definitely feel its a "thing" that players from certain parts of the world can struggle in certain leagues.
And, at this point, Russian and Ukranian players are yet to be really considered a success in the EPL IMO.
For me its a cultural thing, both on and off the pitch. Understanding the way of working and living is massive.
And, for me, its something that should change the more players come and acclimate.
For a long time, a good while back admittedly, Italian players just couldnt seem to work over here. Then Zola, Vialli, DiMatteo came over and broke the mould. Similarly Spanish, was a long time before Spanish players could be considered a real success here (Herrera at Bolton the first to my memory!). And, of course, thats history now.
Its because of that I wouldnt reject a player on nationality. If we were linked to a Ukranian play this January - for sure I would have concerns about how he settles - but I would certainly back his signing still if he looks a good player.