I'm currently playing Assassin's Creed Origins which is set in the 49 BC, with the reign of Cleopatra (which you hel to get the throne). And one of the hint text you get during the load screen says that Cleopatra was the only ruler that learn Egyptian the language of the 7 million citizens of the realm.
So if the Egyptian was the common language, were there any other languages spoken in the realm? And with what purpose?
After Alexander the Great’s conquests, rule over Egypt was passed to his longtime friend, Ptolemy, who was thereafter known as Ptolemy I Soter. Anyways, Ptolemy was a Macedonian, and would have spoken a Macedonian dialect of Greek. He founded the Ptolemaic dynasty, who would continue to speak Greek until Cleopatra’s day. Egyptian was its own language, which would have been spoken by most of the native Egyptians (which does not include any of the Ptolemaic kings). Bayek, the protagonist of AC: Origins, is likely speaking Egyptian throughout the game.
Historians weren’t really able to translate the Egyptian script, hieroglyphs, so our understanding of the Egyptian language was minimal until Napoleon’s expedition to Egypt in 1798, when the Rosetta Stone was discovered. The Rosetta Stone contains a decree from Ptolemy V Epiphanes in 196 BC written in three different scripts: Ancient Greek, Demotic Egyptian and Hieroglyphs. Demotic was a hieratic script, which is cursive variant of hieroglyphs, and was used more for everyday Egyptian than hieroglyphs.