Sometime around 1931-1932 the usage of the term "National Socialist" was forbidden in Soviet Russia, presumably on Stalin's orders. (this is an important topic that researchers reading Russian might usefully pursue, verify, and complete.) After that date, Russian references to Hitler or to National Socialists or to the Third Reich was always to "Fascists" or "Hitlerites." In western Europe and in the United States this terminology was instantly and eagerly adopted by many journalists and political commentators and even political thinkers and historians--wrongly so. It was the only permissible term employed by all Communists, regimes as well as intellectuals, in the Soviet-dominated nations of Eastern Europe.
Stalin had good reasons to insist upon this kind of terminology. National, instead of "international" socialism was more and more applicable to Stalin's Russia in the 1930s, whence it was best to avoid the usage of such a term. At the same time the overall application of "Fascism" to all right-wing and strongly anti-Communist parties and phenomena was very useful for international Communist and left-wing rhetoric and practice.
-John Lukacs, Democracy and Populism: Fear and Hatred p. 117