I don't believe your assumptions about newly conquered people quickly or ever even becoming Latin speakers is correct. Ruling elites maybe. In Roman Judea Greek was a lingua franca of commerce and diplomacy between various peoples. Literate people of the ancient Mediterranean world usually had some Greek. Greeks and the Levant had been interacting for a thousand years before Rome appeared. Greek was considered an intellectual and philosophical language by the Roman world.. Rome did not form many settler colonies in the Eastern Med.