Huehuetlatoani. The Aztec Empire was really three states in an alliance, with a bunch of tributes. The kings of each of those states called themselves Huetlaoni. However, one of those states, Tenochtitlan, began elevating themselves over the rest, and they called their kings Huehuetlatoani. Tenochtitlan was specifically mentioned in events as the capital of the Aztecs, so this has evidently continued (happened earlier?) in the CK2-timeline.
Excan Tlahtoloyan. Literally means "Triple Alliance". One might argue that the CK2-Aztecs were much more centralised around Tenochtitlan, and a name reflecting that might be more appropriate, but I don't speak Nahuatl so Excan Tlahtoloyan will do for now.
Cuauhtlatoani. The historic title for the military governor of a conquered city-state. (meaning "he who speaks like the eagle")
As per
@Brightgalrs: Tonalquizayan, meaning "the land/place where the sun rises"