“Aliens are interrogated by KGB—claimed they were from distant star system—KGB convinced they were lying btw.”
So did the Russians just happen to speak alien, or visa versa.
Great question—the answer to it gives a clue to the riddle.
How do the aliens communicate anyway?
If you know the history of the Betty and Barney Hill “star map” they claimed they received telepathic messages in their heads that gave them a map. In their case the map identified the star Zeta Reticuli.
A variety of “contactees” over the decades have also claimed that different types of aliens communicated with them via telepathy.
A smaller number claimed the aliens could speak their language—and that was claimed by contactees of different countries who spoke different languages.
The most important point—at least imho—is that just because an alien can communicate it is does mean they are telling the truth.
There is a lot of crazy stuff that contactees have indicated aliens have told them over the years.
Imho the communication has happened in many cases—but I think the aliens lie through their teeth.
Here is a good essay discussing why they might do so:
https://thejournalofcosmology.com/Puthoff.pdf
Short version: Most are not from outer space at all. Earth is their planet. We are the trespassers.
If you want to hear contactees speak for themselves this Podcast has a bunch of them:
https://podbay.fm/p/aliens-and-artists