So you know how in episode 3 of this season Daenerys Targaryen shows up at the gates of Mereen...
...and this rider comes out of the city...
...and starts throwing shade, which Missandei translates.
Well here's the thing. The language he's actually speaking is Low Valyrian.
And the words? Well - from an interview with linguist David Pedersen, who created the language:
"There's a scene where the Meereenese rider is challenging Daenerys' champion. He's shouting and Nathalie Emmanuel [Missandei] is translating – but she's not translating what he's saying. He's actually saying a Low Valyrian translation of the French guy's insults in Monty Python and the Holy Grail. That was [series creator] Dan Weiss's idea and it was so hilarious that I had to do it."
Here's the scene:
And here's the Holy Grail scene.