Okay I’m just going to explain out my multilingual Junkrat headcanon cause its one I really really love a lot.
So Junkrat is a very obviously paranoid person in canon, and some one whos very likely extremely smart and learns very well. I personally headcanon him as some one who can absorb a staggering amount of knowledge in a short amount of time if he really sets his mind to it and is interested. I call it a headcanon cause its not confirmed but it seems pretty reasonable for him. But moving on.
Because of his paranoia, I imagine that when he and Roadhog started traveling around the world and Junkrat found himself in countries where englishw as not the first language, he was extremely unsettled about not being able to understand the people around him. For some one used to looking over his shoulder all the time, and probably used to eaves dropping a lot to determine if any ones a threat, language barrier is a bit of a problem. That along with the junkers likely garnering a lot of looks and whispers probably set Junkrat right on edge.
I imagine he just had to deal with it for the first bit, but as soon as he discovered the internet, and sites that teach you new languages, I headcanon him as sitting down and aggressively learning the language of what ever area they ended up in. And thus, resulting in a multilingual Junkrat, who, while he may not be 100% fluent in every language he knows, can understand most of what is said.