Jews living in Egypt spoke Greek - Egypt was massively Hellenized. In fact, the everyday language of one of the largest city's in Egypt, Alexandria, was Greek; not Egyptian, which by the 1st century AD was essentially not the same language as the ancient Egyptians. Like Anglo Saxon England's Norman Invasion which brought French vocabulary and grammar to Old English, Hellenization essentially completely changed the Egyptian language - it now contained hundreds, if not thousands, of Greek words, Egyptian grammar was heavily influenced by Greek grammar, and the entire writing system changed to one based on Greek (this new form of Egyptian is still spoken today - we know it as Coptic). Jews living in the Diaspora tended to live in large cities, not out in the sticks. Much easier to remain as a community in a larger city.
I'm digressing a bit, but in short, Jews in Egypt, like many Egyptians themselves in larger cities, spoke Greek.
