I'm aware of that. I once flew with Iraqi Airways from Bangkok via Bombay to Baghdad, and there were a lot of "guest workers" going to work in Iraq.
Their behaviour was good throughout the flight. I spoke to a couple sitting next to me, and, yes, while it's possible they were technically illiterate, in they sense that they couldn't write, I didn't ask, so I have no idea if they were actually illiterate or not.
But they were perfectly fine as travelling companions. Far better than some "literate" Europeans I've encountered.