I’m not sure that one needs to be able to speak a particular language to be qualified to “teach” it in the manner of instruction used in US public schools. From what I’ve seen, language instruction is just memorization of vocabulary, rules of grammar, conjugations and declensions. There seems to be very little in the way of practical conversation and common usage in the US curriculum for language instruction.
I went to a good Prep School. The course was called Conversational French, and it was very good! Later in college, one of my room mates was Frech, and that’s all we spoke.