On the day of Pentecost, God gave to the disciples the ability to speak in the many different languages of the people of that time. Acts 2:6-11 tells how the unlearned disciples spoke in the languages of the people, and that they were all amazed at hearing the gospel in their own language--not in some unknown tongue that would mean nothing to them.
They didn't have the written word of God at that time--except maybe for whatever Old Testament scripture they may have had, but they had no written words about the birth of the Son of God and the future events as we have now.
Tongues (known languages) were a sign to the unbelievers. They are no longer necessary since we now have the written, inspired word of God for all to read and hear. Some churches even make speaking in tongues a requirement for salvation, and that is just plain WRONG.
Tongues are also seldom (if ever) done correctly. For one thing, there HAS to be an interpreter. Otherwise, they must remain silent in the church to avoid confusion. "If any man speak in an unknown tongue, let it be two, or at the most by three, and that by course, and let one interpret. But if there be no interpreter, let him keep silent in the church, and let him speak to himself and to God." 1 Cor. 14:27,28
So-called "tongues" are more often than not done for the edifying of the speaker only. He/she is seeking praise and admiration of others and wants to appear to be more spiritual than others. One time in a Pentecostal church, everyone (except me) started speaking all kinds of gibberish (that's what it sounded like to me). No one was interpreting any of it, and I doubt that anyone could have done so. One woman near me kept repeating over and over something that sounded like "Ah ditty", in an obvious effort to appear as spiritual as the rest of the people hoped they sounded.
I was very uncomfortable and wanted to leave, but, unfortunately, I was there as someone's guest. I'm sure they wouldn't have noticed if I had driven myself there and just left. They were all too wrapped in in themselves and trying to outdo everyone else in sounding spiritual.