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

for if I pray in an unknown tongue, my spirit doth pray, and my understanding is unfruitful.

What then is it? I will pray with the spirit, and I will pray also with the understanding; I will sing psalms with the spirit, and I will sing psalms also with the understanding;

since, if thou mayest bless with the spirit, he who is filling the place of the unlearned, how shall he say the Amen at thy giving of thanks, since what thou dost say he hath not known?