Public Prayer: should not be Made in an Unknown Language
Source: TTT
1 Corinthians 14:14–16
For if I pray in a tongue, my spirit prays, but my mind is unfruitful. / What then shall I do? I will pray with my spirit, but I will also pray with my mind. I will sing with my spirit, but I will also sing with my mind. / Otherwise, if you speak a blessing in spirit, how can someone who is uninstructed say “Amen” to your thanksgiving, since he does not know what you are saying?