If the Brainless One doesn't speak Goblin then Harry can maybe teach it to say Hermione and they could then discuss or talk about anything without that old foolish meddler understanding them. He does seem to think the world would stop dead without his advice. I personally think he's at least slightly senile or just extremely egotistical if not both. He's also an extreme control freak. He just has to stick his extremely long nose into everybody else's business.