I mean there are immigrant areas in Japan. There’s a big Chinese community in Yokohama, which is reasonably close to Tokyo.
But I guess that would involve interactions with working class Chinese immigrants, or second generation kids of immigrants. And that’s not the type of people some fancy rich kid would want to be around.
What kind of racism do you need to assume Japanese people simply know how to speak Mandarin and also use it in their daily lives? And what kind of racism do you need to not even investigate this. They could have sent the kid to Singapore or Malaysia, a lot of people speak Mandarin there.