Cappadocian Greek is Greek heavily mixed with Turkish, to the extent that is arguably better viewed as a distinct Hellenic language rather than just a nonstandard Greek dialect. However, around a century ago, most Greek speakers were expelled from Turkey and deported to Greece (and the same happened in reverse, most Turkish-speakers in Greece were deported to Turkey), including almost all Cappadocian-speakers - and they and their descendants largely switched to standard modern Greek - with the result that it was long believed that Cappadocian had died out in the 1960s, although more recently it has been discovered that there remain small populations of Cappadocians in rural Greece keeping the language alive.
Are there really any other Hellenic languages besides Greek?