The Mandarin Teacher is the teacher at Eddie, Emery, and Evan's new Chinese school for the episode So Chineez. He is a very angry and strict teacher who says everything in Mandarin. There are intentionally no English subtitles in the episode attached that translate what he's saying.
He also immediately gave Eddie, Emery and Evan a quiz on their first day, despite that they don't know Mandarin yet.
The last time he was seen, he was mad at Eddie for some unknown reason.