“It’s better if the teacher can’t speak the student’s first language.” Really?

I’ve been in the teaching game since 2011. My experience is mainly teaching Japanese students, along with a smattering of Chinese and Korean folks who are based in Japan. Several times now, I’ve come across the belief that “Native English teachers shouldn’t be able to speak the learner’s first language. It’s better that way, because then the learner will be forced to communicate only through the target language.”

Not “teachers shouldn’t speak the learner’s L1.” They “shouldn’t have the ability” to do so.

I find this to be a very strange distinction, because of course the goal is to get the learner to use the target language as much as humanly possible in a given lesson. This means if the learner straight-up asks me, “How do you say 海外 in English?” I answer with, “Can you explain the word to me?” The learner then comes up with something like…