Lengua isn't a fancy name. In the context of tacos, it's the appropriate term. Lengua is Spanish for tongue, and tacos are Mexican. Where they speak Spanish.
It's equivalent to saying chorizo tacos instead of sausage tacos. But go on and enjoy that high horse.
Hell yeah! I swear, the best eating on any animal is above the shoulders. Cow tongue is also great in curry and other stews.