Adam Clarke on 1 Corinthians 14:11

If I know not the meaning of the voice - Την δυναμιν της φωνης, The power and signification of the language.

I shall be unto him that speaketh a barbarian - I shall appear to him, and he to me, as a person who had no distinct and articulate sounds which can convey any kind of meaning. This observation is very natural: when we hear persons speaking in a language of which we know nothing, we wonder how they can understand each other, as, in their speech, there appears to us no regular distinction of sounds or words. For the meaning and origin of the word barbarian, see the note on Act 28:2.