Maybe you should try studying 1Cor 14 and its context...
A clue, the context is stated in 1Cor 14v19: "yet in the church..."
Paul esteemed the gift of tongues very highly and used it at great length in private prayer! 1Cor 14v18...
No one is apposing the gift of prophecy hearing the clear words of God . Its the sign as to who it points to and what it confirms that is the issue.
There is no outward sign of prophecy other them that men believe God.
The sign is in respect to those who do not believe prophecy in any language to include Hebrew . As God was bringing prophecy (God's word) with words they could understand 33000 heard the interptation of God and entered the kingdom of God . Those who mocked God, the unbelieving Jew (no faith ) God with Stammering lips or mocking words brought prophecy in the language of all the nation he was drawing . And yet for all that they still refused to belive prophecy . They were hopping the Hebrew tongue was the tongue of God and they followed the order of Jeremiah 44 and saw no evil
As for the word that thou hast spoken unto us in the name of the Lord, we will not hearken unto thee.But we will certainly do whatsoever thing goeth forth out of our own mouth, to burn incense unto the queen of heaven, and to pour out drink offerings unto her, as we have done, we, and our fathers, our kings, and our princes, in the cities of Judah, and in the streets of Jerusalem: for then had we plenty of victuals, and were well, and saw no evil. Jeremiah 44:16-17
Private prayer our silent prayer , I am sure that Paul used words thoughts according to verse 9. speaking into the air with words that have no meaning would be fruitless I believe.
Some think it holds some sort of mystic power and confirms they have a special relationship with God and therefore they seek after it in vain repetitions . No secret prayer language
So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken?
for ye shall speak into the air.1 Cor. 14:9