Wait, what do you mean with no point of reference? If you were physically there the whole world would be your point of reference. You could point at a rock and make a grunting sound and somebody would eventually tell you the word for “rock”. They’d have actual teachers. How you would go about accessing them is anybody’s guess, but hey, they’d exist.

The hard part would be learning it when there’s nobody left to speak it because making grunting sounds in the general direction of rocks is famously ineffective at decoding ancient documents.