early 15c., in reference to classical history, "a non-Roman or non-Greek," earlier barbar (late 14c.) "non-Roman or non-Greek person; non-Christian; person speaking a language different from one's own," from Medieval Latin barbarinus (source of Old French barbarin "Berber, pagan, Saracen, barbarian"), from Latin barbarus "strange, foreign, barbarous," from Greek barbaros "foreign, strange; ignorant," from PIE root *barbar- echoic of unintelligible speech of foreigners (compare Sanskrit barbara- "stammering," also "non-Aryan," Latin balbus "stammering," Czech blblati "to stammer").
Greek barbaroi (plural noun) meant "all that are not Greek," but especially the Medes and Persians; originally it was not entirely pejorative, but its sense became moreso after the Persian wars. The Romans (technically themselves barbaroi) took up the word and applied it to tribes or nations which had no Greek or Roman accomplishments.
Also in Middle English (c. 1400) "native of the Barbary coast;" meaning "rude, wild person" is from 1610s. Occasionally in 19c. English distinguished from savage (n.) as being a step closer to civilization. Sometimes, in reference to Renaissance Italy, "a non-Italian." It also was used to translate the usual Chinese word of contempt for foreigners.
Barbarian applies to whatever pertains to the life of an uncivilized people, without special reference to its moral aspects. Barbarous properly expresses the bad side of barbarian life and character, especially its inhumanity or cruelty: as, a barbarous act. Barbaric expresses the characteristic love of barbarians for adornment, magnificence, noise, etc., but it is not commonly applied to persons: it implies the lack of cultivated taste .... [Century Dictionary, 1889]
late 15c., "uncultured, uncivilized, unpolished," from French barbarique (15c.), from Latin barbaricus "foreign, strange, outlandish," from Greek barbarikos "like a foreigner," from barbaros "foreign, rude" (see barbarian (n.)). Meaning "pertaining to or characteristic of barbarians" is from 1660s. Related: Barbarically.
Perhaps a native name, perhaps an Arabic word, from barbara "to babble confusedly," but this might be ultimately from Greek barbaria. "The actual relations (if any) of the Arabic and Gr[eek] words cannot be settled; but in European langs. barbaria, Barbarie, Barbary, have from the first been treated as identical with L. barbaria, Byzantine Gr[eek] barbaria land of barbarians" [OED].