How could we get Islam to spread across Mesopotamia and North Africa while maintaining the local languages and cultural identities? Plenty of regions that were Islamized later, like Iran, Indonesia, and Senegambia managed to adopt the faith while retaining their native languages... So, for example, why not have an Egypt that still speaks (and writes) in a form of Coptic? What would be the effects of an "Islamic World" without an "Arab World"?