1 Corinthians 14:10 There are, it may be, so many kinds of voices in the world, and none of them is without signification. 11 Therefore if I know not the meaning of the voice, I shall be unto him that speaketh a barbarian, and he that speaketh shall be a barbarian unto me.
1 Corinthians 14:10 should end any idea of tongues being a bunch of mumbo-jumbo jibberish. Paul calls tongues “voices in the world.” Moreover, these “voices” have “signification.” They mean something to someone somewhere on earth. A voice is not just a sound; it is a sound that carries a message. Therefore, every voice is significant because of the message it carries. For example: Look at what the disciples spoke on the day of Pentecost. A careful bible reader will easily see there is no “special heavenly prayer language” here.
If we don’t know what is being said, then the speaker is like “a barbarian” to us. Nowadays, we think of a “barbarian” as someone who is an uncultured oaf. But in the Bible, a barbarian was someone who didn’t know the spoken language of the time. A “barbarian” was a foreigner to the languages of civilization.
 Acts 2:4-6 “And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. 5 And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. 6 Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language.”