In the church at Corinth, why did those who spoke in tongues not simply translate their own prayers, instead of needing an interpreter?

This text is from a letter written by David Gooding in 1991.

I am very interested in your suggestion that a tongues speaker always knew well enough what he was saying, and could have repeated the very same message in plain, straightforward language, understood by everybody if he so cared.

My reading of the text had suggested to me that 1 Corinthians 14:14 declares that when somebody prays in a tongue, that person's understanding is unfruitful. That is to say, he does not understand with his intellect what he is saying, and therefore his intellect gets no edification from it. On the other hand, he is presumably edified in some other way; and that is what is meant in 1 Corinthians 14:4, 'He who speaks in a tongue edifies himself'.

There is nothing essentially wrong with edifying oneself, of course; but if the edification cannot be passed on to the church, then the speaking in tongues is forbidden in the church. That, I say, has been my understanding hitherto.

Ever truly yours,