I only use Slavo-Turk as a way to refer to the region from Slavia to the region around the Black and Caspian Seas.
While the Khazar conversion is a major theme of medieval Rabbinic literature, it is not significant and most of the conversion in the Black & Caspian Sea area took place long before Turkic peoples wandered into the area.
Turk is just short Helleno-Pontic-Armenian-Irano-Scythian-Caspian-Turkic region. Conversion to Judaic religion is well-attested in the region in ancient literature (including the Bible), and there probably was some minor Turkic-Tatar conversion (including the Khazar conversion) in the region shortly before the area became Islamic (as is described in Jewish, Byzantine, and Arabic literature).
Slavia refers to the region where there were Knaanic-speaking Judaic populations as well as the historically attested conversions that took place among Slavic-language speakers during the time of the Hussite Rebellion and later. RASHI's commentaries contain a few Judeo-Slavic or Knaanic words, and this presence suggests there was export of Slavo-Turk Judaic/Jewish population into French Jewish (Gallo-Roman) population in the 11th century. Export of Slavo-Turk Judaic/Jewish population into the Ibero-Berber and the Syro-Mesopotamian community is attested from the 10th century.
The replacement of the earlier Talmudic term גרממיא (Germamya) by Ashkenaz suggests that between the 10th and 13th century Slavo-Turk Judaic/Jewish merchants came to dominate the overland route from France to Mesopotamia. This trade route was extremely important until the Mongols destroyed Baghdad and rampaged into Poland.
Yiddish probably starts as a relexification of Knaanic to the mostly Germanic vocabulary of a lingua franca or pidgin used for communication between Slavic & Germanic speakers in areas where Slavic & Germanic peoples cohabited. The oldest stratum of Yiddish contains obsolete Christian terminology. The semantics of Yiddish is almost entirely Slavic while the grammar is strongly Slavic.
We can be completely certain that ancient Judeans never left Palestine, gradually converted first to Christianity then to Islam, and became the ancestors of modern Palestinians.
People of the ethnic background of Dabakr and of my family must be considered invaders, interlopers, thieves, and genocidaires in the Levant.
I tend to consider Alexandrian Koine to be an ancient Greek dialect. I could be incorrect, but I was under the impression that some specialists in historical Greek linguistics considered Griko to descend from Doric Greek. The Ophitic variant of Pontic Greek has characteristics that cause some specialists to classify it as a pre-Koine dialect or an evolution of ancient Greek separate from Koine.
The Greek Diaspora population like the Jewish Diaspora population has a large mercantile component but unlike the Jewish Diaspora population had a central origin population that continued to exchange individuals with the Diaspora communities, and there was a linguistic leveling effect.
The Jewish Diaspora descended from Mesopotamian, Greek, Phoenician, Armenian, Slavic, Germanic, and other convert populations had no major connection with the mostly agrarian Judean population, which had entirely converted to Christianity or to Islam by the 13th century. The mercantile elements used written Rabbinic Hebrew to communicate. Because this written Rabbinic Hebrew was a relexified version of the writer's native language, miscommunications was always possible, but the problem tended to be alleviated by commercial use of quotations that came from sacred texts and that had agreed meanings.
(In the Slavo-Turkic culture area from Eastern France to the Ukraine, there was a leveling effect, in that Ostjiddisch replaced Knaanic & was moving westward. Judeo-French dialects long ago died out or were supplanted by West German Jewish dialects.)