A.T. Robertson Commentary 1 Corinthians 14:11

"If then I know not the meaning of the voice, I shall be to him that speaketh a barbarian, and he that speaketh will be a barbarian unto me." — 1 Corinthians 14:11 (ASV)

The meaning of the voice (την δυναμιν της φωνης). The power (force) of the voice.

A barbarian (βαρβαρος). Jargon, βαρ-βαρ. The Egyptians called all βαρβαρους who did not speak their tongue. The Greeks followed suit for all ignorant of Greek language and culture. They divided mankind into Hellenes and Barbarians.

Unto me (εν εμο). In my case, almost like a dative.