'There are, it may be, so many kinds of voices in the world, and no kind is without signification. If then I know not the meaning of the voice, I shall be to him who speaks a barbarian, and he who speaks will be a barbarian to me.'
Indeed the world has many voices that speak (he avoids the word 'tongues' specifically so as not to confuse the issue), and each one means something. And yet if I do not know the meaning of the voice I will be to that one simply as a barbarian, someone who does not know his language, and he will be a barbarian to me, because I do not hear his language. Non-Greek speakers were thought of as 'barbarians' simply because their language sounded to the Greeks like 'bar-bar-bar'. The whole point is that that is what tongues sound like to the church as a whole. They were a meaningless jabber.