Pretty much every country teach english in school nowdays. Im not sure does russian schooling systems have low standards or something, but I have played probably closer to 100 mmo/online games during my lifetime and its always the russians who struggle to speak even the most basic english, if any. Main reason to seperate russians, is purely to avoid people flooding english speaking channels with russian language. That has happend so many times in mobile games in the past, like in era of legends, where turkish speaking players were a big problem aswell during the launch. Its hard to do content with people, who doesnt even speak english.