In his book "Legend: The Secret World of Lee Harvey Oswald," Edward J. Epstein says Oswald asked for and was given on February 25, 1959, a Russian language proficiency exam, and that he scored a lot better than he should have done if the allegation that he'd been teaching himself the very difficult language for only three months was true. Therefore, Epstein believes that Oswald either had a Russian-language tutor or had started learning Russian while still in Japan.
After the assassination of JFK, Oswald's fellow Marines reported being incredulous when they saw him several times with a beautiful "round-eyed" Eurasian woman in Japan.
Is it possible that the KGB or the GRU recruited the Marine U-2 radar operator in Japan (where the Communist Party was legal) and told him that he'd be going to The Worker's Paradise?
Author John M. Newman says in his book, "Uncovering Popov's Mole," that CIA's spy, GRU Lieutenant-Colonel Pyotr Popov, told his handler in West Berlin in April of 1958 that he'd recently overheard a drunken GRU colonel boast that the Kremlin had all of the top-secret specifications of the U-2 spy plane. Newman says that Bruce Solie in the CIA's mole-hunting Office of Security was himself a "mole" and that he sent (or duped his confidant, protégé, and mole-hunting subordinate, James Angleton, into sending) Oswald to Moscow in 1959 as an ostensible "dangle" in a planned-to-fail hunt for "Popov's Mole" (Solie) in the wrong part of the CIA.
Ironically(?), Popov was arrested in Moscow on the same day that Oswald arrived there -- 16 October 1959.