To add a bit - modern tongues-speech, non-cognitive non-language utterance, is actually not gibberish. Gibberish by its nature does not seek to mimic language; tongues-speech does.
I don't think it would be possible to demonstrate (linguistically) that the modern phenomenon is language. In order for something uttered to be language, regardless of where spoken (the US, some remote island in the middle of nowhere, some alien planet, the spiritual/heavenly realm), or by whom spoken (human, alien, spiritual being), it must contain at minimum two distinct features; modern tongues-speech contains neither.
Another possibility is that the miracle was on the ears of the hearers. It is quite possible that if you were there what the 120 were speaking would sound to you like the tongues you may have heard in a pentecostal or charismatic gathering, what you have been saying sounds like gibberish to you.
That is why the OTHERS mocked them and said that they were drunk.
It is quite possible that people from different nations might have heard the
same disciple speaking and each heard them in their own language.
It is possible that some of them realized this was going on and that their wide eyed "what meaneth this" was because their Elamite neighbor was understanding the same person speaking as the Pamphylian next to him was understanding and they were even the more confounded because that they all understood the same speakers and so it was obvious that a great miracle was going on beyond their comprehension to make sense of. It is one thing to hear someone speak in your native language, but to realize that all the other foreigners understood him in their own language? Well then What Meaneth This Indeed!
Now this is not a stretch or a strain of the text. It is a plain interpretation based on the text that is quite miraculous and possibly a correct interpretation. I did not invent this interpretation. You will read about it as a possibility in commentaries from time to time. I am not sure if there is anything in the Greek that would exclude it as a possibility.
4And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
5And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven.
6Now when this was noised abroad, the multitude came together,
and were confounded, because that every man heard them speak in his own language. 7And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans?
8A
nd how hear we every man in our own tongue, wherein we were born? 9Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia,
10Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes,
11Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God.
12And they were all amazed, and were in doubt, saying one to another, What meaneth this? 13Others mocking said, These men are full of new wine.
There is a lot of being 'confounded, amazed, marvelling, and being in doubt to the meaning of it' for it to be just that you are hearing a man from Galilee speak in your own language. Especially if you do not know the men, you just know that they are Galilaeans. I would think that your first thought would be "Oh nice, they have been practicing our native tongue to make us feel welcome and now they are going to tell us something about God in our own tongues" But would you be confounded, amazed, marvel and be in doubt as to what it all means? Probably not. However if you heard Nathaniel speaking in your native Mesopotamian, and next to you A man you met for breakfast that morning from Egypt also understanding Nathaniel in Egyptian, well then.. You would be Amazed, marveling, greatly confounded trying to make sense of ... How Can This Happen? What does it mean? So I lean toward this understanding.
I think to the OTHER mockers, it sounded like what you hear today.
From this point on, all of the other instances of tongues there were no foreigners who heard it in their own native language, it would have just sounded like tongues with no interpreter, the Samarians, the Ephesians, the House of Cornelius, Paul, the Corinthians. There are no hints of people from other nations being at Corinth and hearing someone in their own language. I think that only happened at Pentecost. All the other times are examples of what we can expect when believers are baptized in the Holy Spirit. There will be no foreigners that hear in their own language. The initial experience requires no interpreters. The personal prayer requires not interpretation. In the assembly when one person speaks out during the appropriate time for others to hear, someone with the gift of interpretation will receive it from the Holy Spirit on the spot and give it and all will be edified. There is no need for a translator of foreign languages to be present as that is NOT the gift of interpretation and the tongue is not a foreign language as they were not in the Corinthian church, house of Cornelius, Ephesus, Samarians.
And I propose they were not just the 120 each speaking one foreign language in Acts 2 but rather that each speakers was understood by those who heard them in their own language but others thought they were babbling just like people who really speak in tongues today get accused of.
I cannot prove this interpretation is the perfect one, but until I have a reason to see it otherwise this is what I think happened on that day. I am trying to "listen to the Spirit in the Text" If I see that I have violated any rules of hermeneutics in this interpretation I will correct it and line up my interpretation with any clarity I discover.