The speaking in tongues that is recorded in the Bible was the speaking in other people’s language. This is what the Bible says that happened the first time that the Holy Spirit descended on the apostles. When they spoke in tongues, those who heard them heard them in their various native languages in which they were born.
As religious practices and expansion increase, we are having another form of speaking in tongues. Christians who are speaking in tongues are now speaking what nobody knows what they are saying. It is no more the type of speaking in tongues which the apostles had.
Acts 2:4, 7-8 (KJV) And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans?
And how hear we every man in our own tongue, wherein we were born?
In this video, Bro Eli Soriano re-emphasizes that the speaking in tongues which the Bible is talking about is speaking in another man's language. Bro Eli said that while the apostles were speaking in their Galilean tongue, those who heard them were hearing them in their own mother’s tongue.
It is the truth as we all have it in our various Bibles. Those apostles were understood by those who heard them. They didn't learn the language. They didn't know what they were saying but they were understood by those who heard them. It was the Holy Spirit who gave them the utterances.