HZ: Approximately how many languages have you invented at this point?
DAVID PETERSON: I think I've invented over 50 languages at this point. Not all of them are very large in terms of vocabulary size, and not all of them are very good. I had created about 17 before I ever started working on Game of Thrones.

HZ: The languages you hear in Game of Thrones: Dothraki -

[CLIP] Khal Drogo: “Moon of my life, are you hurt?”

HZ - the various dialects of Valyrian:

CLIP: Daenerys: “Valyrian is my mother tongue.”

HZ: - those aren’t the actors making up some gibberish. Those are functional languages, with large vocabularies and complex grammars and etymologies.