Because of the way the question is framed, a Liar is forced to answer the same way as a Truth Teller, since he must lie about the lie he would have told if you asked him this question. Since it makes no difference whether the native is a Truth Teller or a Liar, we now get to assume without loss of generality that the native is a Truth Teller. This simplifies the analysis quite a bit.

Negating the meaning of "arg" negates the correct answer to the question in each case, but it also negates the way the Truth Teller must express this answer. It therefore has no net effect on the answer a Truth Teller gives in each case. We now get to assume without loss of generality that "arg" means "yes."

A Truth Teller will answer "arg" (yes) if the fork goes to the Truth Tellers' village, and "zog" (no) otherwise. Take the fork you're pointing to if and only if he answers "arg".

You may go on your way without ever knowing the meaning of the native's answer or whether he told the truth.