The irony is that Stalin, was also a “National Socialist”, in that he rejected Lenin and Trotsky’s “Internationalism” in favor of “Socialism in One Country” with the Russians the “Master Race” (although Stalin himself was Georgian). He ordered the “Russification” of the entire Soviet Union, replaced native populations with ethnic Russians in the most prosperous regions.
Stalin believed in establishing "socialism in one country" rather than prioritizing world revolution, but he was not an ethno-nationalist of any kind ideologically.
The reason Stalin Russified Soviet Republics was not because he believed in a Russian "master race" to rule over Central Asian or Baltic peoples, but because he wanted to replace the ethno-national identities of these Republics with a generic, Russian-speaking "Soviet Man" with only a Soviet/Communist identity. It would be equivalent to Brussels making English (or Esperanto, while they're at it) the official language of the EU to suppress the individual identities of European countries.