1st Answer: In the Na'vi language it's called Toruk, which means "Last Shadow". Its proper name is the Great Leonopteryx.
2nd Answer: Yes, in Na'vi it's called Toruk, but Great Leonopteryx isn't actually the "proper" name. It is a name humans created for that bird. But the proper name would be Toruk because the Na'vi people live with that bird, and it's their bird to name. Sorry if this is confusing.