“It’s also not unreasonable to assume they cannot speak english...isn’t it?”
Actually, it is.
Their job is to train U.S. marines...presumably most of whom do not speak arabic. Also, we are told these men were Iraqi-Americans...live in the U.S....better than good chance they know English.
I’m fairly sure, that if you were to travel with Americans that go to different countries to train individuals in the native tongue, that you would find them speaking english amongst themselves. That is what people normally do.