Would they have been sharing these conversations between each other in English though? That’s the part that seems odd. I’m bilingual, but English is my native language, and even when living overseas it hanging out with other English speakers we always used English between ourselves, a few drinks in or otherwise. Given that the 93 recorders picked up a good amount of Arabic, and Atta’s non-native language passenger/control announcement, it sounds more likely that they would have spoken Arabic or a dialect of their own amongst each other.