"Mr Crouch? He speaks over two hundred! Mermish and Gobbledegook and Troll ..."
-- Percy Weasley (GF7)
The goblin language.
“Bladvak” means “axe” in Gobbledegook (GF24). Miranda Goshawk’s original The Book of Spells was translated into Gobbledegook (BoS).
Harry, Ron, and Hermione hear Goblins conversing in their native language; it struck them as being "a rough and unmelodious tongue, a string of rattling, guttural noises..." (DH15).
Mr. Crouch (GF7) & Dumbledore (BLC) both speak this language.