I wrote to tech support last week with this problem. That Russian is not in the list of available languages. The technical support employee seemed to understand the essence of the problem and promised to bring it to the developers. For now, I can offer you a simple solution to this problem. In the file </home/username/.config/spotify/prefs> after the line <core.clock_delta = 0> added the parameter <language = "ru"> and after restarting the application the Russian language appeared.