The Russians (you mean Soviets) did nothing to preserve yiddish. They tried to exile the jews to a desolate remote corner on the fringes of siberia where they could practice their culture (not their religion) in a soviet communist framework.

I took Yiddish in university for a while. During the soviet years they tried to neutralize any hebraic or biblical references. For example, in hebrew the word for friend is "Chaver". It's the same in yiddish. But the soviets insisted that it be changed to the more germanic "fraynd". Similiarly, they insisted even on the changing of spellings to make the language altogether less hebraic and jewish - and more neutralized and soviet.