There was, maybe still is, a type of speaking in tongues that could be called a “private prayer language.”
We should not let the spectacle of contemporary charismatics cause us to delete chapter 14 of First Corinthians.
1 Corinthians 14:2,14,15
2 For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries.
14 For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.
15 What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also.
My issue is that, while I believe all the gifts of the Spirit are still available today, the speaking in tongues that I hear by Pentecostal believers typically all sounds the same, like they are imitating each other. It generally tends to sound like a variation of Aramaic.
So I refrain from mocking or condemning anything that could be a genuine manifestation of the Holy Spirit, if it has a biblical basis.
However, slaying in the spirit and the Toronto Blessing activities of shaking the head, acting drunk, barking like a dog, rolling on the floor, “holy laughter”, etc. are things that I reject as unbiblical.
In 1 Corinthians 14, speaking in tongues is never called ecstatic, babbling, or uncontrollable.
I accepted Christ at a Mennonite church camp as a teenager. As I read my Bible, I saw mentions of speaking in tongues. When I asked the pastor who led me to Christ about tongues, he said it was a valid thing, but he did not talk about speaking in tongues because it was divisive in the church.