I have heard many Greeks and not Greeks that the word barbarian (in Greek varvaros) called the people that :
1-Were not Greeks
2-They didnt speak the Hellenic language or the Greek dialects.
Many ancient writers (specially Greeks) used this term in them work to describe other nation (usually the Persians and Pelasgians).
But some others Greeks used to insult other Greeks (e.g. Athenian Demosthenes against Spartans, Macedonians e.t.c.)
What from the above is true?
I think Strabo has gave the correct etymological meaning of the barbarian in the ancient period.
[14,II,28]I suppose that the word "barbarian" was at first uttered onomatopoetically in reference to people who enunciated words only with difficulty and talked harshly and raucously, like our words "battarizein," "traulizein," and "psellizein";for we are by nature very much inclined to denote sounds by words that sound like them, on account of their homogeneity. Wherefore onomatopoetic words abound in our language, as, for example, "celaryzein," and also "clange," "psophos," "boe," and "crotos," most of which are by now used in their proper sense.
Accordingly, when all who pronounced words thickly were being called barbarians onomatopoetically, it appeared that the pronunciations of all alien races were likewise thick, I mean of those that were not Hellenic.
Those, therefore, they called barbarians in the special sense of the term, at first derisively, meaning that they pronounced words thickly or harshly; and then we misused the word as a general ethnic term, thus making a logical distinction between the Greeks and all other races.
The fact is, however, that through our long acquaintance and intercourse with the barbarians this effect was at last seen to be the result, not of a thick pronunciation or any natural defect in the vocal organs, but of the peculiarities of their several languages.
And there appeared another faulty and barbarian-like pronunciation in our language, whenever any person speaking Hellenic did not pronounce it correctly, but pronounced the words like barbarians who are only beginning to learn Hellenic and are unable to speak it accurately, as is also the case with us in speaking their languages. This was particularly the case with the Carians, for, although the other peoples were not yet having very much intercourse with the Greeks nor even trying to live in Hellenic fashion or to learn our language--with the exception, perhaps, of rare persons who by chance, and singly, mingled with a few of the Greeks --yet the Carians roamed throughout the whole of Greece serving on expeditions for pay. Already, therefore, the barbarous element in their Hellenic was strong, as a result of their expeditions in Greece; and after this it spread much more, from the time they took up their abode with the Greeks in the islands; and when they were driven thence into Asia, even here they were unable to live apart from the Greeks, I mean when the Ionians and Dorians later crossed over to Asia.
The term "barbarize," also, has the same origin; for we are wont to use this too in reference to those who speak Hellenic badly, not to those who talk Carian. So, therefore, we must interpret the terms "speak barbarously" and "barbarously-speaking" as applying to those who speak Hellenic badly. And it was from the term "Carise" that the term "barbarize" was used in a different sense in works on the art of speaking Hellenic; and so was the term "soloecise," whether derived from Soli, or made up in some other way.