1 Corinthians 14:4-5, Speaking with Interpretation
A person speaking in an unknown tongue will not help to build up the spiritual life of others in the church unless there is proper interpretation. With interpretation, the amount of content conveyed would be reduced by half when there is a need for translation. Unless there is a grave need because the majority of the congregation needs interpretation to a language they would understand and the preacher is unable to do so in that language, an interpreter would benefit the congregation.