Note 13 at 1 Cor. 14:28: If there is no interpreter present within the church, then the one with the gift of tongues is to keep silent (see note 12 at this verse). He is encouraged to speak quietly to himself and to worship God. Although his gift does not benefit the church without an interpretation, there is much benefit to the private practice of tongues, or as it's stated here, within the church "let him speak to himself and to God " (vv. 4, 14, 16-17). Softly praying and praising God in tongues in the assembly, as private prayer, is certainly in order.

However, the practice common in many Spirit-filled churches, of everyone praying in tongues loudly at the same time, is not consistant with Paul's instructions here. The people should always be able to be understand the person leading the service unless he is delivering a message in tongues, which should then be interpreted. An individual should not be distracted from the service through another praying in tongues unless it is interpreted.