As Paul wrote, 1Cor. So the third criteria is that the tongue be interpreted. If tongues are spoken in a way so as to be heard by someone else, it must be interpreted. We've seen tongues' languages, what they are saying, who they are speaking to, the numerical limitation on them, and the requirement of an interpretation. Paul writes, 1Cor.
Tongues are for a sign to unbelievers.
Now remember, if tongues are abused or faked, unbelievers say you're crazy. But if tongues are inspired by the Spirit, they are a sign to an unbeliever. Don't forget what a powerful sign the tongues were to the unbelieving multitudes in Acts 2. The same way. I'll give you two examples to illustrate.