Soviet Union multilingual
The former Soviet Union was initially formed with 12 republics, three of which were of Slavic origin (RSFSR, Ukraine and Belorus), Moldova and other Asian republics. As we see, the variety of languages was extreme in the same way as state boundaries. The Soviet Union occupied 1/6 of the whole earth surface being the largest state in the world.
Consequently, it united millions of different nations and ethnicities that had completely different cultures, values, social, political, religious experience, whatever. So, how did the Soviet power manage to hold the keys? Perhaps, it had a progressive interethnic policy that provided the freedom of thought, confession, expression and so on? But the problem was solved in a different way.
In fact, there was no clearly-formulated state interethnic policy that would "cross the i's and dot the t's". There was no diversity of ethnic languages, but the main state language (it was Russian). The Russians as an ethnicity were the basic foundation of Communists as a political force. It was the Russians that brought them to power and they constituted the largest ethnicity group in the former USSR. That's why the Kremlin relied on the Russians first and foremost.
To a certain degree, the national languages and cultures were developed but that was very insignificant compared to the real needs of the local population.
Unsurprisingly, the most part of the population is well aware of Russian even long after collapse of the Soviet Union.
