'I thank God, I speak with tongues more than you all. Howbeit in the church I had rather speak five words with my understanding, that I might instruct others also, than ten thousand words in a tongue.'
He sums up the point from his own example. It is not that he is against tongues, in fact he uses them frequently. Indeed he can thank God that he is sure that he speaks with tongues more than all of them. (So let them not think that they are so very special).
But in the church he would prefer to speak only five intelligible words in order to instruct others than to speak ten thousand words in a tongue which is not understood Thus he follows his own guidance.
(These words in fact throw a great light on Paul's prayer life. This confidence must arise because of the hours he spent in private prayer. He was clearly certain that it was more than those Corinthians who thought themselves 'ultra-spiritual'. And as he also prayed equally as much with the understanding it demonstrated how much he prayed, although he does not point the fact out specifically. He leaves them to infer it).
We note from this that he considers that genuine tongues are composed of words, and thus are languages of a kind. And the previous verse has suggested that a main use of tongues is thanksgiving, so that we are beginning to get some idea of what tongues are.