While a bit clunky (because Astruc and the writers probably didn’t have a backstory in mind when they first came up with Gorilla’s character, and because the English translation of the show opted to have it stated that everyone is speaking English in-universe despite following a bunch of French people living in France), I do love that Miraculous Ladybug essentially gave us an explanation for why Gorilla never speaks. In season 5, episode 24, Representation, Felix just offhandedly mentions that in addition to the magic jewelry and petty rivalry between his dad and Adrien’s, he also owes his existence to Colt handing over his best “knight” to serve as Adrien's protector in exchange for the use of the peacock miraculous. And just like that a light goes on: Gorilla doesn’t speak because he’s American. And not one that up and moved to a whole ass new country by choice! No one named names, but Gabriel didn’t leave any wiggle room for Colt to give him someone who already had an interest in relocation. Gabriel demanded the best of the best, and shucks to them if they don't speak the langauge! Poor Placide I.T. (aka, Gorilla before little kid Adrien decided to rename him) had his whole life derailed because Emilie wanted to help her sister have a baby, and Gabriel was too petty to do it without getting something in return, and we don’t even know if he knew a single word of French before being told to pack his bags.
It's so sad, but also kind of funny, because of course he’s probably learned the language over the years since becoming Adrien’s bodyguard. Even if he doesn’t feel confident or feel the need to speak, he can probably understand most of what’s said around him. But then we have characters like Marinette, who have a tendency to frantically vomited out words in sudden gusts that just get more and more rapid and embarrassing with every breath, and we can only assume that while she’s standing there mortified and hurriedly saying one thing and then another, Gorilla is actually just trying to pick out the last word he understood in all the mess.
He's not staring at her because he's rude or because he's judging her. He just can't understand her when she's talking so fast!
