if we can determine who is not random with our first question, lets say we find that C is not random, then we can ask C "is A truth?" then ask C "is B truth?" His answer will either be "Ww, Ww" or "Ww, Uu" or "Uu, Ww" or "Uu, Uu." When it is either "Ww, Ww" or "Uu, Uu", he is the truth. Also we have determined, depending on which he uses, the translation of "No." Now we can solve it with the language barrier with just four questions by simply asking C, "is A (or B, doesn't matter) random (or the liar, doesn't matter.) But if C answers "Ww, Uu" or "Uu, Ww" we know he is the liar and we are still in the dark with the language, so we have to ask him "is A (or B, doesn't matter) the liar?" He will always answer in the affirmative, which breaks down the language barrier... then we have to ask one more question.

Still not sure we have a question that can determine that one of them in particular is not random, and it takes me 4 or 5 questions still...