Many have asked what the Bible says about speaking in tongues.
What many churches call "speaking in tongues" today is nothing like what the Bible records in the books of Acts and Corinthians. The miracle that occurred on the Day of Pentecost in A.D. 31 (Acts 2:4-8 Acts 2:4-8  And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
 And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven.
 Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language.
 And they were all amazed and marveled, 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?
American King James Version×) was one of communication—apparently both in the speaking and the hearing. The Greek word translated "tongues" is glossa and means "languages." The miracle of speaking in tongues meant that every member of the audience could hear in his or her native tongue (language, see Acts 2:9-11 Acts 2:9-11  Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia,  Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes,  Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God.
American King James Version×).
Also, some in the early Church, particularly in Corinth, had the ability to speak in different languages. In that case, it seems that people were showing off their abilities, speaking every language they could, regardless of whether the people who heard them could understand. They were caught up in their vanity, having lost sight of the fact that one should always use spiritual gifts to serve others. Paul wrote chapter 14 of 1 Corinthians specifically to deal with this problem. He pointed out that the proper use of the gift of languages would be to speak the language or languages that the congregation could understand. It would be like speaking Spanish to a Spanish-speaking audience or French to a French-speaking audience.
Paul reminded the Christians in Corinth that speaking different languages was of no real value if an audience could not understand the words. He admonished them to concentrate more on understandable communication than on their linguistic abilities.
All biblical examples of speaking in tongues stand in stark contrast to the type of "speaking in tongues" done in some churches today, where the speaker utters a "language" that sounds like gibberish, not an actual human language.
In other letters, Paul and John warn Christians not to be taken in by spiritual-appearing phenomena, indicating that demon spirits sometimes imitate spiritual gifts in an attempt to confuse people (1 Timothy 4:1 1 Timothy 4:1Now the Spirit speaks expressly, that in the latter times some shall depart from the faith, giving heed to seducing spirits, and doctrines of devils;
American King James Version×; 1 John 4:1 1 John 4:1Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
American King James Version×).