Paul writes, “Yet in the church I would rather speak five words with my understanding, that I may teach others also, than ten thousand words in a tongue” (1 Cor 14:19). Paul is referring to preaching (prophecy) in tongues, not prayer in tongues. When there is no interpreter, the speaker should keep quiet and “speak to himself and to God” (1 Cor 14:28). Thus, Paul discourages preaching in tongues without interpretation but never discourages praying in tongues during service (see 1 Cor 14:39)
Paul says that “God is not the author of confusion but of peace” because during church service in Corinth, the members would preach in tongues even when there was no interpreter and many would speak at once (see 1 Cor 14:27-30). All this caused confusion and disorder.
Prayer in tongues is directed to God and needs no interpretation (1 Cor 14:2). When everyone prays in tongues during church service, there is no confusion nor disorder. Rather, there is a spirit of unity.