The correct option is C Though, yet
The sentence expresses a contrast between the possibilities "he has learned many languages" and "he does not know Chinese", because even though he has learned many languages, "he" does not know Chinese. Hence, the pair of conjunctions that expresses contrast/opposite meaning is used, and that's option C. "Though, yet" both are conjunctions that express contrast, hence option C is correct. "Either, or" is used when a sentence expresses a choice between two possibilities, and here there's no choice, because both the possibilities of 'learning many languages' and 'not knowing Chinese' are true. Hence option A is incorrect. "Neither, nor" is used when none of the possibilities in a sentence are true, whereas the possibilities in the given sentence are both true, hence option B is incorrect. "Both, and" is used when the possibilities in a sentence are both true, but they're not contrast in meaning, when they're contrast the pair of conjunctions used is "though, yet". Hence option D is incorrect.