"which were nothing but gibberish."
Yes, this has been proven by linguists, that it is ecstatic speech and does present with any of the markers of a "language."
It is amazing to me that it still persists in this day and age, speaks to the power of deception, I guess.
In science, or even social science 'research', let's be careful about using the word 'proven'. That's not how it works, and that type of language is unscientific given the parameters of the research. These linguists did not test all speaking in tongues or, to my knowledge, any samples which were identified by others who spoke the language.
Also, the scriptures speaks of 'tongues of men and of angels'. There are other 'extreme possibilities' as a part of the argument. Giving one's body to the burned is _possible_. So is giving all to the poor. (Has anyone seen that old 60's or 70's movie where St. Francis even gives away his clothes?) Why would 'tongues of angels' be impossible?
The underlying assumption is that linguists have identified variables of human speech clearly enough, the variables by which speech is inflected for meaning, to test their speaking in tongues samples against these variables.
Of course, if a tongue were 'tongues of angels' linguists would have to gain a knowledge of angelic language(s), including the variables by which meaning is inflected in the language(s) in a broad enough sense to identify the utterances against angelic speech. To my knowledge, linguists have not performed such research on angelic speech.
There were different researchers, but one researcher's argument was that some of the prayers were given in a monotone high pitch, not like human speech, but I knew a Canadian girl who prayed in English just like that, and most tongues I'd heard didn't follow that pattern.
Now if some speaking in tongues is genuine, and some is fake, the research does not prove there is no genuine speaking in tongues. The early Pentecostal movement grew partly because people would go to Azusa Street and other meetings and hear their own languages. The newsletter of the movement reports many such testimonies. Dr. Vinson Synan interviewed individuals who were children at Azusa Street, and one of them pointed out that the reason the meetings grew is that people would come and hear speaking in tongues in various languages. I remember she mentioned Japanese.
I can think of two other books that contain testimonies written by other individuals by there. Fire on Azusa by Val Dez tells of a woman hearing Russian 'in tongues.' There was another account in 'The Comforter has Come.' You can also look up The Apostolic Faith newsletter on the Flowers library site to read the various accounts of such things in there.
I've also had conversations with at least three people who either heard a language they knew in tongues or the 'tongue' they were speaking was identified by someone who understood the language. One is a German I correspond with who heard speaking in tongues (one in KJV English) by Europeans two who didn't know English.
Another was a daughter of a missionary. I 'd just read that the missionary had heard Chinese villagers speaking in English during his mission trips there. She visited my church and sang there; her husband preached. I mentioned what I'd read about her father, and she'd heard a little Chinese grandma speaking in tongues in a village in China.
Another was a missionary who'd previously served among the Navajo before going overseas. Back when he did native ministry, he got invited to preach to the Cherokee. He had a strong urge to speak in tongues while preaching, which he perceived to the the Holy Spirit and eventually yielded to it. Afterward, someone asked how he spoke their language. He'd rebuked some youths who had planned some mischief-- firecrackers under the stage or cutting the tent ropes or whatever it was.