What are barbarians?

Ancient Greek βάρβαρος (bárbaros, “foreign, non-Greek, strange”), possibly onomatopoeic (mimicking foreign languages, akin to English blah blah)

The word عَجَم (ʕajam, “non-Arabs”) is from a pre-Islamic form أَعْجَم (ʔaʕjam), from the root ع ج م (ʕ-j-m), referring to people who speak unclearly

Mleccha (Sanskrit: म्लेच्छ, romanized: mlecchá) is a Sanskrit term referring to those of an incomprehensible speech, foreigners or invaders deemed distinct and separate from the Vedic tribes.

Inherited from Proto-Slavic němьcь (“foreigner, German”), from němъ (“mute”)