Russian language

Russian was a human language spoken by humans in the nation-state of Russia and in some areas that were part of the former Soviet Union on Earth. Russian was Slavic in origin.

After the death of Captain Spock, Doctor Leonard McCoy held Spock's katra, and broke into Spock's quarters. Upon discovering this, Chekov made several statements in Russian upon discovering the break-in. (TOS movie Star Trek III: The Search For Spock).

When Sybok entered into a mind meld with Pavel Chekov, Chekov would later come to believe that Sybok spoke to him in Russian. (Novelization of Star Trek V: The Final Frontier).

The dedication plaque of the starship SS Tsiolkovsky was written in Russian. (TNG episode The Naked Now).