The right/left distinction is less meaningful in authoritarian single-party regimes. The Soviet Union and Maoist China were obviously economically leftist, but politically, authoritarian regimes often align in similar ways, regardless of their economical policies. Pro-nationalist policies are favored by them because they're useful to their purposes; you wouldn't want your influence being diluted by outside cultural and economic forces.

That’s an overly cynical view in the context I mentioned above. Lenin was advocating for more language rights and cultural self-development opportunities for the non-Russian peoples of the Russian Empire years before he had any glimmer of hope of seizing power. At that time, the “authoritarian single-party regime” that leftism in Russia opposed was the tsarist rule, which didn’t permit any local autonomy until after the 1905 Revolution, and even then only grudgingly.