Question

he speaks _____ deferent language u
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Answer 1

Answer:

What is the difference between Speak English and Speak in English?

Which one is (more) acceptable in this sentence:

"You must speak English/ in English in class."

Or, are both correct? If yes, what is the difference?

Another question:

I know it is incorrect to say to talk English. What about to talk in English? Can you use it instead of speak in English?