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

For if I pray in an unknown 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 when thou shalt bless with the spirit, how shall he that occupieth the room of the unlearned say Amen at thy giving of thanks, seeing he understandeth not what thou sayest?