Thematic Bible: Should not be made in an unknown language

For if I pray in a tongue, my spirit prayeth, but my understanding is unfruitful. What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also. Else if thou bless with the spirit, how shall he that filleth the place of the unlearned say the Amen at thy giving of thanks, seeing he knoweth not what thou sayest?