The western coast had been Greek for nearly 2 millennia by the battle of Manzikert in 1071 ad. The rest of the peninsula had used Greek for administrative and literary purposes since the conquests of Alexander in the 4th century bc though once the region became integrated into the Roman Empire Latin was used for official documents. Latin was officially replaced with Greek again in the 7th century ad though this had little effect on the general population as they had been speaking Greek for centuries. There were also the Armenians who had done quite well under the Macedonian dynasty and had spread into eastern Anatolia during the 10th and early 11th century ad. The battle of Manzikert and its aftermath pushed the Greek speaking Byzantine Empire to the nothern and western coasts of the peninsula but it would be several more centuries until the Ottoman Turks were able to exert complete political control over the peninsula. It's important to understand that the Turks did not purge or forcibly convert the regions captured as the Greeks provided an urban source of taxation and of skilled artisans to the nomadic tribes fresh off the steppe. The Greeks living in the areas had to choose whether to emigrate to the regions still held by the empire or stay in the Turkish held territory without the benefits provided by the Byzantine government but with a generally lighter tax burdern. Here is an ethic map I found of Turkey before the Armenian Genocide and mass deportations of the World War 1 and the 1920s. It should give you an Idea of what things might have looked like before Manzikert.