The Cappadocian Greeks traditionally spoke a dialect of the Greek language known as Cappadocian Greek.
Cappadocian Greek diverged from the other Byzantine Greek dialects early, beginning with the Turkish conquests of central Asia Minor in the 11th and 12th centuries, and so developed several radical features, such as the loss of the gender for nouns.
However, having been isolated from the crusader conquests (Fourth Crusade) and the later Venetian influence of the Greek coast, it retained the Ancient Greek terms for many words that were replaced with Romance language ones in Demotic Greek.
After centuries of Ottoman rule the Turkish language began to emerge as the dominant language of Cappadocia.
Many Greeks began to speak Turkish as a second language and became bilingual, this was the case with the “Kouvoukliotes” who were always Greek speakers and spoke Turkish with a strong Greek accent, and there were Cappadocian Greeks who only spoke the Turkish language and had given up the use of Greek centuries earlier, known as the Karamanlides.
At the beginning of the 20th century, the Cappadocian Greek language still had a strong presence at Gülşehir (formerly Arabison/Arapsu) north-west of Nevsehir, and in the large region southward as far down as Niğde and Bor.
Greek was also still spoken at Silli north-west of Konya, in Pharasa (today's Çamlıca village in Yahyalı district) and other villages in isolated communities in the interior of central Turkey prior to the Genocide of 1915 and subsequent population transfers.
Many Cappadocian Greeks completely abandoned Greek when they learned Turkish, although in the western regions of Cappadocia many Greeks still retained their native language.
John Robert Sitlington Sterrett travelled through Cappadocia in 1884 and noted: "Melegobi is a large and flourishing village, inhabited almost exclusively by Greek-speaking Greeks.
The Greeks are numerous all through the western part of Cappadocia, and generally cling to their language with great tenacity, a fact worthy of notice, inasmuch as the Greeks in other parts of Asia Minor speak only Turkish.
Instances of Greek-speaking towns are Niğde, Gelvere, Melegobi (Μελοκοπια), and Ortaköy in Soğanlı Deresi."
In the early 20th century scholars and linguists studying the Cappadocian Greeks observed that many Cappadocian Greek villages had begun to replace their native Greek language for the Turkish language.
During the 19th-century British scholar John Pinkerton was informed by the Turkish-speaking Greeks that past Turkish rulers of Anatolia had caused them to lose the knowledge of the Greek language, Pinkerton reported that:
..."the cruel persecutions of their Mahomedan masters have been the cause of their present degraded state of ignorance, even in regard to their native tongue; for that there was a time when their Turkish masters strictly prohibited the Greeks in Asia Minor even from speaking the Greek language among themselves, and that they cut out the tongues of some, and punished others with death, who dared to disobey this their barbarous command.
It is an indisputable fact, that the language of their oppressors has long since almost universally prevailed, and that in a great part of Anatolia even the public worship of the Greeks is now performed in the Turkish tongue.
The following works, in the Turkish language, but all in the Greek character, afford further proof of what I have now stated...” (John Pinkerton, 1817) 
In the 1920s when the Cappadocian Greeks arrived in Greece, the Cappadocian Greek spoken by them was hardly intelligible with the Demotic Greek used in mainland Greece, as it had been cut off from the rest of the Greek-speaking world for centuries.
The Cappadocian Greeks were more linguistically Turkified then the Greeks in Pontus and the western coastal regions of Turkey.
Once in Greece though, they started using the modern Greek language, causing their ancestral Greek dialect, the Cappadocian Greek language, to go to the brink of extinction.
The Cappadocian Greek language was believed by some scholars to have been extinct
The Cappadocian Greeks traditionally spoke a dialect of the Greek language known as Cappadocian Greek. Cappadocian Greek diverged from the other Byzantine Greek dialects early, beginning with the Turkish conquests of central Asia Minor in the 11th and 12th centuries, and so developed several radical features, such as the loss of the gender for nouns. However, having been isolated from the crusader conquests (Fourth Crusade) and the later Venetian influence of the Greek coast, it retained the Ancient Greek terms for many words that were replaced with Romance language ones in Demotic Greek. After centuries of Ottoman rule the Turkish language began to emerge as the dominant language of Cappadocia. Many Greeks began to speak Turkish as a second language and became bilingual, this was the case with the “Kouvoukliotes” who were always Greek speakers and spoke Turkish with a strong Greek accent, and there were Cappadocian Greeks who only spoke the Turkish language and had given up the use of Greek centuries earlier, known as the Karamanlides. At the beginning of the 20th century, the Cappadocian Greek language still had a strong presence at Gülşehir (formerly Arabison/Arapsu) north-west of Nevsehir, and in the large region southward as far down as Niğde and Bor. Greek was also still spoken at Silli north-west of Konya, in Pharasa (today's Çamlıca village in Yahyalı district) and other villages in isolated communities in the interior of central Turkey prior to the Genocide of 1915 and subsequent population transfers. Many Cappadocian Greeks completely abandoned Greek when they learned Turkish, although in the western regions of Cappadocia many Greeks still retained their native language. John Robert Sitlington Sterrett travelled through Cappadocia in 1884 and noted: "Melegobi is a large and flourishing village, inhabited almost exclusively by Greek-speaking Greeks. The Greeks are numerous all through the western part of Cappadocia, and generally cling to their language with great tenacity, a fact worthy of notice, inasmuch as the Greeks in other parts of Asia Minor speak only Turkish. Instances of Greek-speaking towns are Niğde, Gelvere, Melegobi (Μελοκοπια), and Ortaköy in Soğanlı Deresi." In the early 20th century scholars and linguists studying the Cappadocian Greeks observed that many Cappadocian Greek villages had begun to replace their native Greek language for the Turkish language. During the 19th-century British scholar John Pinkerton was informed by the Turkish-speaking Greeks that past Turkish rulers of Anatolia had caused them to lose the knowledge of the Greek language, Pinkerton reported that:
..."the cruel persecutions of their Mahomedan masters have been the cause of their present degraded state of ignorance, even in regard to their native tongue; for that there was a time when their Turkish masters strictly prohibited the Greeks in Asia Minor even from speaking the Greek language among themselves, and that they cut out the tongues of some, and punished others with death, who dared to disobey this their barbarous command. It is an indisputable fact, that the language of their oppressors has long since almost universally prevailed, and that in a great part of Anatolia even the public worship of the Greeks is now performed in the Turkish tongue. The following works, in the Turkish language, but all in the Greek character, afford further proof of what I have now stated...” (John Pinkerton, 1817) 
In the 1920s when the Cappadocian Greeks arrived in Greece, the Cappadocian Greek spoken by them was hardly intelligible with the Demotic Greek used in mainland Greece, as it had been cut off from the rest of the Greek-speaking world for centuries. The Cappadocian Greeks were more linguistically Turkified then the Greeks in Pontus and the western coastal regions of Turkey. Once in Greece though, they started using the modern Greek language, causing their ancestral Greek dialect, the Cappadocian Greek language, to go to the brink of extinction. The Cappadocian Greek language was believed by some scholars to have been extinct
Cappadocian Greeks