I beg to differ a little bit here. I had the experience to exchange words both in my native tongue (whether in-body of out-of-body, I knowth not) and in giberish to some supernatural entities.
Now I suspect that I might know what the nature of "speak in tongue" is.
Once your soul gets out of your body, the language barrier is simply gone. When one speaks to multiple audience, they all hear their own first/native language. Through this mechanism you shall know that we are created and God exists, or else this is simply impossible.
That's how souls talk to each other. Now there are some people who are born to be able to see the "ghosts" often. This is actually a result of certain part of their soul slidely deviates from their body. Some buddhist even practise to achieve this kind of deviation to have a sneak peek on the other side. So with a "visually" soul deviation you see "ghosts". Seeing ghosts actually means those supernatural entities (spirits) can establish a communication channel by manifesting themselves visually to the one with a soul deviation.
Now how about a soul deviation in the "speaking" and "hearing"? There are also two different situations here, 1) a in-born deviation, and 2) a deviation made by God the Holy Spirit.
Case analysis:
category 1. in-born soul deviation in the speaking part
You can speak in tongue. In effect, you speak either in your first language or in giberish but abit out-of-body. It is just a slide deviation or else you can both speak and hear when you totally out-of-body.
category 2. in born soul deviation in the hearing part
You can interpret who speaks in tongue, as whoever in category 1 speaks with soul deviation, you hear your own first language. So that you can tell other what he speaks (in the speaker's first language or giberish)
For example, a spanish speaks in spanish but since he speaks with a slide soul deviation, an english in category 2 will hear English so that he can intepret what the spanish says to other englishmen.
category 3. God the Holy Spirit is in influence
Now both the speakers and listeners are under a slide soul deviation initiated by God. In this case, the language barrier is half gone. It is a half gone because the speakers may not be able to listen while the listeners may not be able to speak (in tongue). I suspect that this is the case of the Pentecost situation.
I can't say that the following verses supporting my view.
Acts 26:14 (NIV)
We all fell to the ground, and I heard a voice saying to me in Aramaic, 'Saul, Saul, why do you persecute me? It is hard for you to kick against the goads.'
Acts 26:14 (KJV)
And when we were all fallen to the earth, I heard a voice speaking unto me, and saying in the Hebrew tongue, Saul, Saul, why persecutest thou me? it is hard for thee to kick against the pricks.
Acts 22:9 (NIV)
My companions saw the light, but they did not understand the voice of him who was speaking to me.
Acts 22:9 (KJV)
And they that were with me saw indeed the light, and were afraid; but they heard not the voice of him that spake to me.
Acts 2:6-8
When they heard this sound, a crowd came together in bewilderment, because each one heard them speaking in his own language. Utterly amazed, they asked: "Are not all these men who are speaking Galileans? Then how is it that each of us hears them in his own native language?