As I continue my parallel study of the Greeks and the Romans, I learned some interesting aspects about the use of Greek language by elite Romans during the Republic and in the early Imperial period.
Dr. Robert Garland, in his lecture series " Greece and Rome: An Integrated History of the Ancient Mediterranean ", related that one of the first efforts of Roman ambassadors attempting to speak Greek was met by derision by the Greeks of the Greek colony of Tarentum just prior to the war with Pyrrhus. Dr. Garland says the ancient sources point to this humiliation as one of the reasons for the war.
But as Roman exploits extended into mainland Greece and the Hellenistic Kingdoms where Greek was the lingua franca of business and law, and thousands of highly educated Greek slaves flooded Rome, including teachers, the elite of Rome began learning Greek in earnest.
By the late Republican period, most Roman senators spoke Greek and only a few "boorish" exceptions, as recounted by Cicero, required a translator. However, Cicero still claimed that Latin provided the ability to be more precise in formal rhetoric. Dr. Garland said there were no Greek or Roman dictionaries at the time but such dictionaries have since been compiled and the actual tally of words is about 90,000 for Latin and over 130,000 for Greek so he felt this disproved Cicero's assertion.
Bilingualism continued until the separation of the empire into East and West. Then Dr. Garland points out that bilingualism died out quite quickly in the West. I found this puzzling as interaction with the Greek East still continued. But, I have read in other sources that formal education was no longer emphasized as much among the elite in the west during the late imperial period leading up to the Dark Ages and perhaps this is the reason.
Dr. Garland pointed out one other interesting effect continuing Roman conquest had on the speaking arts. By Augustus' reign, there were so many different languages spoken by the common people in Rome that when mime and pantomime theater was introduced, it became far more popular than the traditional Greek theater presentations.