I speak for myself and from my own experience, speaking in tongue is just a soul speaking language. Humans' language barrier is gone once leaving the body. "Speaking in tongue" is a common language spoken by souls without a body. When you speak in your own native tongue, everyone (soul) else will hear as their own native tongue. Souls even communicate with angels this way. Once enabled (can be disabled under different circumstances), you can hear the angels speaking in your native tongue.
The Pentecost event is rather a temporary enabling of this soul-to-soul speaking mechanism by God the Holy Spirit.
On the other hand, the Corinthians' way of speaking in tongue can be a way of praying in an unknown tongue, that is, not actually a human language. To identify or distinguish the two, a interpreter is needed,
1 Corinthians 14:27-28
If anyone speaks in a tongue, two—or at the most three—should speak, one at a time, and someone must interpret.
If there is no interpreter, the speaker should keep quiet in the church and speak to himself and to God.
It means, at the time of speaking, both can possibly be gibberish as it's supposed to be an off-body language. More like though, the speaker is trying to speak in his own native language, but it turns out to be in gibberish (equally possible is that, it's not gibberish but just his native tonuge), while at the same time all other people will hear as their own native tongues.