1 Corinthians 14:13 YLT

¹¹  if, then, I do not know the power of the voice, I shall be to him who is speaking a foreigner, and he who is speaking, is to me a foreigner;

¹²  so also ye, since ye are earnestly desirous of spiritual gifts, for the building up of the assembly seek that ye may abound;

¹³  wherefore he who is speaking in an 'unknown' tongue -- let him pray that he may interpret;

¹⁴  for if I pray in an 'unknown' tongue, my spirit doth pray, and my understanding is unfruitful.

¹⁵  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;