One day, Pyrolysis runs into Tristão and they hit a snag already, they cannot speak each other's language. However, right away, Tristão gets to explaining his situation without words, just gestures, props, and vocalizations. Pyrolysis quickly understands that Tristão is saying he has no money, no good job, and no way to do anything about it. Since Pyrolysis can speak to ponies, he explains the situation to those Tristão is working for and he helps him get a better job that doesn't require communication. Tristão is very grateful to Pyrolysis for the help and the two end up hitting it off afterwards as friends, and eventually, yes, as romantic partners.
They may not be able to speak each other's language, but they still communicate through other means, wordlessly. Vocalizations, gestures, props, acting, even just touch. Words aren't important to them. This dynamic is very loosely based on a song.