you're weird af
he is not expanding any horizons by learning a language that distant and niche
he is learning it because he watched too much anime
you automatically expand your horizon by learning a different, difficult language and processing huge amounts of new information
by the way, you don't even know if he'll use Japanese. maybe he'll want to move here some day in the future.
anyways it's weird to shit on the guy for wanting to learn something new.
eat your fish and chips and relax bud