I don't recall ever eating a hog's tongue, but I have eaten beef tongue many times when I was younger. We never skinned them cold...that is, without being cooked first.
My mother would cover the tongue with water, then heat to just below boiling, and simmer it for a long time... I think it took 3-4 hours. Then she would remove it and allow it to cool somewhat. She always made sure to skin it while it was still warm, said it was a lot harder when it was cold. I would guess hog tongue would be much the same.
A beef tongue has a...disturbing taste when the skin is left on.
