Tongues are in modern day, divided into 2 categories.
One, it is an angelic language meaning that it makes no common
sense to another person but it is language inspired by the Holy
Spirit inside a christians to communicate with God. Yes it sounds
gibberish to others, ev en to the person who speaks it becos it is
the Spirit in him/her speaking not him or her.
Two, it is a known language but maybe p r e v iously unknown to the
speaker. For example, i may not know French or some African
language, then the Spirit came upo n me and then suddenly I get the
gift to speak French, that is tongues too. IT can be an oneoff
situation i n this case.