Commonly known as 'Speaking in tongues', glossolalia is practiced by many Pentecostal and Charismatic Christian groups around the world. They take their cue from biblical passages in the New Testament that refer to the apostles being charged by the Holy Spirit so that they could speak languages they did not understand yet could be understood by their audience. Technically this would be Xenoglossia - speaking in actual languages unfamiliar to the speaker. Some ministers or priests claim to be able to translate the 'words' to reveal the will of God, which of course often resembles the views of said minister or priest.
Several studies have been done on the brain state of practitioners when they are in the act and other studies have been done on the language and syntax of their utterances. Quite often what is being said is a form of language, in that it presents the common patterns of speech, especially of the speakers native language. It has noticeable syllables and sentence structures and it uses the common vowel and consonant sounds familiar to the speaker. However there is no proper structure or regular pattern that can be ascribed to concepts or objects. Essentially it is meaningless gibberish that resembles the speaker's native language.
According to Robert Carroll of the Skeptics Dictionary: "There is evidence that while speaking in tongues people experience a sharp decrease in frontal lobe function, the area of the brain that enables reason and self-control. There is also increased activity in the parietal region of the brain, which takes sensory information and tries to create a sense of self relating to the world". There are lots of interesting videos of people speaking in tongues, go give them a watch to experience it. Some people have a natural ability to do it, others learn it from an early age and retain the ability even after abandoning their religious faith. Why not try it yourself and see if you can do it?