Try not to make it political or bring in the discussion on civil war. I was just playing around with Facebook stats for advertisers and found that 81.3% of Ukrainians use Facebook in Russian. Anyone who published ads on Facebook can check it themselves in the Ad Manager.
BTW, 92.86% of Belarusians use Facebook in Russian. And there's no "Belarusian" among language choices there, so the rest should be covered by English and a fraction of a percent for Polish.