http://moq7aejnf4xk5k2bkaltli3ftkhusy2mbrd3pj23nrca343ku2mgk4yd.onion/about
At least it should be not, yet I see that many Russians don't understand Ukrainian like at all, which is surprising for me. I accidentally learnt it just by consuming content in it with help of a dictionary to look up some words that are archaic in Russian or have different etymology. As for Belarussian, situation is the same, but I don't speak it, just know some words I have accidentally memorised while listening to music.