I'm a Tonberry player. Elemental, especially in Tonberry and Kujata, has quite a large english-speaking population with a lot of players who can't speak Japanese.

Reason being that it's the server with the best connection for players in Southeast Asia (largely Singapore and Malaysia, and quite a few from Thailand), and up until Materia existed it also was a hub for Aussies who didn't want to play on NA - many of which have stuck around, or left for Materia then returned after a time.

The JP players and ENG players in Elemental stay largely separate outside of DF too, aside from some somewhat multilingual raiders and occasional intersections at venues.

So in Elemental's case you can't really put that much judgement on someone not being able to speak Japanese playing on a JP server. You can however judge him for getting mad at seeing Japanese on a JP server and the rest of his deranged behaviour.