Speaking in tongues is used by some church leaders and denominations 'on the fringe' in order to identify themselves as having the Holy Spirit inside them in the same way as it was in the apostles on the Day of Pentecost. But when we read Acts 2, we find that the 'tongues' which they spoke were unknown only to the apostles themselves. The hearers identified every language they used in their message as the hearers' native tongues.
I've known this 'speaking in tongues' belief to have caused actions which were, to put it bluntly, fraudulent. I was familiar with the Catholic Missal when it was still written in Latin. One of my fellow Christians, who was also familiar with the Missal, went to a meeeting circa 1971 where a traveling evangelist was speaking. But the way it worked was that the evangelist would speak in an unknown tongue, and then one of the preachers with the gift of translating tongues would interpret what the evangelist had said.
What the evangelist did was quote from a section of the Catholic Missal (he had obviously memorized it), and then repeat those pages two or three times. But afterwards the preacher got up and 'translated' what the evangelist had said as telling the people that God had blessed their particular denomination, the laity was to obey without question whatever commands the heirarchy of that church gave them, and they were to see all those who weren't members of that church as condemned by God himself. And there were quite a few people there who accepted that propaganda as having come from the Holy Spirit himself, since it was a 'translation' of what they believed was the Holy Spirit's speaking through the evangelist in a tongue which the hearers didn't recognize, except for my fellow Christian.