In other words, when someone natively speaks a language that doesn't include /f/ or /v/, and they try to pronounce those sounds in English but don't entirely succeed, what sound do they end up producing?
Context: I am writing a story about harpies, whose language is roughly based off of Ancient Greek. (In the story, their language and writing system greatly influenced proto-Greek languages, from Phoenician to Attic.) In Ancient Greek, there is no "f" or "v" sound; those sounds only exist in Modern Greek. I am wondering, when trying to pronounce an English word, what sound are these harpies likely to produce when trying to mimic the /f/ and /v/ sounds, which do not exist in their native language?
Obviously, I don't expect to find native Ancient Greek speakers, but hopefully there are those of you who speak languages with similar phonologies, who are better versed in phonetics than I am, and/or who know more about Ancient and proto-Greek languages than I do.
Thank you in advance!