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

For if I pray in a tongue, my spirit prayeth: but my understanding is without fruit.

What is it then? I will pray with the spirit, I will pray also with the understanding, I will sing with the spirit, I will sing also with the understanding.

Else, if thou shalt bless with the spirit, how shall he that holdeth the place of the unlearned say, Amen, to thy blessing? Because he knoweth not what thou sayest.