OK. There are tongues of men &
angels, which denotes what would be an unknown tongue.
1Cor 14:
13Therefore,
one who speaks in a tongue is to pray that he may interpret. 14For if I pray in a tongue, my spiritprays, but my mind is unproductive.
15What is
the outcome then?
(1) I will pray with the spirit, but I will pray with the mind also; (2)
I will sing with the spirit(worship), but I will sing with the mind also.
16For otherwise, if you
bless God [g]in the spirit only, how will the one who occupies the place of the
[h]outsider
know to say the “Amen”
at your giving of thanks, since he does not understand what you are saying?
17For you are giving thanks well
enough,but the other person is not edified.
18I thank God, I speak in tongues more than you all;
19nevertheless, in church I prefer to speak five words with my mind so that I may instruct others also, rather than ten thousand words in a tongue.
Tongues are used for personal & corporate worship, instruction, edification, & comfort. The reason is plain why we should interpret them: No one knows what's being said otherwise.
It's sad that the modern church abuses them ignorantly for self edification.