Maybe this will help: https://en.wikipedia.org/wiki/Language_of_the_New_Testament
"Koine Greek, the common language of the Eastern Mediterranean[3][4][5][6] from the Conquests of Alexander the Great (335–323 BC) until the evolution of Byzantine Greek (c. 600)."

and

"The New Testament Gospels and Epistles were only part of a Hellenistic Jewish culture in the Roman Empire, where Alexandria had a larger Jewish population than Jerusalem, and Greek was spoken by more Jews than Hebrew."