Bible Verses About Public Prayer: Should not be made in an unknown language

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?