The game is entirely in English.
They do not speak English.
It’s not really necessary for a Mario game.
This is word for word exactly the first reply I expected to get when I posted this. The fact that they had fewer words to translate makes the fact that they didn’t bother translating them worse, not better.
Nintendo has never been great in this regard. They tend to rely on game design for accessibility
Clearly you’ve never heard the German super Mario Brothers song.
I found a YouTube link in your comment. Here are links to the same video on alternative frontends that protect your privacy: