I’ve started reading Kotkin’s Stalin (thanks, jamessal!), and was struck by this passage on his linguistic accomplishments as a youth:
At the same time, Georgia was a diverse land and the future Stalin picked up colloquial Armenian. He also dabbled in Esperanto (the constructed internationalist language), studied but never mastered German (the native tongue of the left), and tackled Plato in Greek. Above all, he became fluent in the imperial language: Russian. The result was a young man who delighted in the aphorisms of the Georgian national poet Shota Rustaveli (“A close friend turned out to be an enemy more dangerous than a foe”) but also in the ineffable, melancholy works of Anton Chekhov[…].
Of course, in later years Stalin would execute Esperantists en masse, as we discussed here.
Addendum. Another linguistic tidbit:
Many of Russia’s Muslims spoke a dialect of Persian, but most spoke Turkic languages, giving Russia several million more Turkic speakers than the “Turkish” Ottoman empire.