Well, they speak Arabic, but most Arab-speakers today had ancestors who spoke other languages.It is as if the people of Britain had chosen to given up their own languages for Latin, the language of the Roman conquerer, or taken up Norman French.
Early Arabs were Nabateans, I believe, also conquered by the Roman Empire. They were inveterate traders. When they landed in Portugal, THEY named it "bortugal," which means "orange" in Arabic, since it was the first time the Arabs had seen the citrus orange.
The Arabs have no "p" in their alphabet so it sounded like Bortugal, but was later elided into Portugal.
Even some Portuguese guides didn't know that bit of information about their own country.