Speaking in tongues is something that is largely practiced by charismatic groups such as the Pentecostals.
They'll often claim that they're vocalizing a divine language unknown to the speaker
and that it's an evident token of being filled with the spirit. The point to Acts chapter 2 is their proof text.
The problem with this is that the Bible never exemplifies speaking in tongues as being an incoherent expression only known to God.
On the contrary, Acts chapter 2 shows us that it's referring to a known language.
The Bible says in verse number 4,
You see the miracle is that God gave the apostles the ability to preach the word of God in a language they previously did not know before.
What these people are doing is simply demonic.