Talking in tongues is one of many ways to produce an altered state simply and easily.
It has no more relationship to any particular religion or belief than breathing does.
It is spontaneously uttering in a form which is felt as a language, as though it were your native tongue.
I can't remember exactly when I first discovered it myself, but I have had some great sessions. I once heard a sufi teacher chanting the first part of the muslim shahada - la ilaha il allah - and that is awesome to dive right into. Being something like a tongue twister it requires a lot of focussed attention and that plus the sound you are making is mesmerising.
I suggest that you
just imagine you know a totally unique personal language, and start talking in it. You may feel self-conscious and a bit awkward at first, but just carry on until you are doing it thoughtlessly. Singing or rapping in tongues over a musical or percussive background is a good option to learn to
enjoy the experience. Allow the experience to be driven by whatever feelings arise, and express those feelings without reference to thoughts and beliefs.
It is an excellent way to allow expression of emotion, and to map out your feelings and especially any blocked emotions. Because there are no words, it frees you from conceptual mind and the neurolinguistic patterning which has set like glue around your mind. I think the activity allows a deeper level of language and 'inner dialogue' to be directly experienced, without the judgements and evaluations which otherwise accompany thought (and by extension, prayer).
Try it out away from other people. Keep it to yourself. Don't start up on a bus or in the park or you may be carted off in a straight jacket.
Vary your approach - Try it very softly under the full moon by the sea, try it loudly in the mountain forests, use it to talk to an imaginary alien who replies telepathically from Sirius
Really. What I mean is allow the experience to take you outside your box.
I had an amazing surprise one day, listening to the radio. Some Cree people from Canada were in Australia about 20 years ago attending an international youth festival in Darwin. When I heard their native tongue i was shocked and amazed at how similar it is to my own natural form of uttering.Not sure what that means, but it felt good for some reason.
It can help to learn some simple mantras in sanskrit, or short prayers in aramaic/hebrew/arabic, or aboriginal or native American songs. That is something like learning different kinds of scales if you are a musician - each kind of sound will produce personal inner responses, and help to educate the part of your brain that is using it to express.
Being an electronic music maker, one approach I've tried to loosen up the language centre is to record phrases of my normal speech in a wave editor, then reverse it and learn to imitate it. You can have fun with this. Then record the phrase you have learned to say backwards.
Reverse it and listen - this will give you the original phrase back, if you have said it properly (quite tricky to do). This really reeducates your brain-tongue circuit.
The way you speak just about defines your reality. Loosening it up is like yoga stretches for your hidden psychoanatomy.