Someone that is Russian speaking should give some insight actually...
It's not so easy to judge anyone that posts a lot in a foreign language sub forum if you don't speak that language yourself.
What do you want to know? Ratimov is one of the most reputable members of Russian board who makes lot of important things in different ways which make our local board better. If it wasn't so you'd seen this in some of these topics also, because there's enough users from Russian board who are active enough in English sections. If you have any other questions, then please specify what do you want to know.
Well I gravitate towards the opinion that OP is at least exaggerating his accusations.
But if Ratimov is indeed a serial plagiarizer I'm sure a Russian speaker would be more able to tell if this is true or not since he is so active on the Russian subforum.