This morning I learned that the first two syllables in the word Barbarian, which derives from the Greek word Bárbaros, represents the sound a foreign language made to Greek ears. Barbar is somewhat similar to our blah blah. Persian, Egyptian, even the dialect of Greeks living at the edges of Greek influence–it all sounded barbaric to the Greeks. And to Athenians all other Greeks were probably barbarians.
So, one side claimed everyone else was a Barbarian, and the other side replied that it all sounded Greek to them.