Spiritual gifts - speaking in other languages/tongues

This is a tricky one.The gift of other languages, or tongues as it is often referred to, is the ability to speak in languages that you haven't learned. Some people believe this refers to a heavenly language, and others believe that it refers to foreign languages. 1 Corinthians 14 talks about this gift.

The gift of other languages is speaking to God.
1 Corinthians14:2
Those who have the gift of speaking in a different language are not speaking to people. They are speaking to God. No one understands them—they are speaking secret things through the Spirit.

It benefits you, not the rest of the church.
1 Corinthians 14:4
Those who speak in a different language are helping only themselves.

The gift of prophecy is greater because it instructs and encourages the believers.
1 Corinthians 14:5
I would like all of you to have the gift of speaking in different kinds of languages. But more, I want you to prophesy. The person who prophesies is greater than the one who can only speak in different languages—unless someone is there who can explain what he says.

​It is for non-believers like the gift of miracles.
1 Corinthians 14:22
So the gift of speaking in different kinds of languages is a sign for those who do not believe, not for those who believe.

Only two or three people should speak in tongues and take turns.
1 Corinthians 14:27
When you meet together, if anyone speaks in a different language, then it should be only two, or not more than three, who speak. They should speak one after the other.

Someone should interpret what is spoken in tongues, or you should be quiet.
​1 Corinthians 14:27b-28
And someone should interpret what they say. But if there is no interpreter, then anyone who speaks in a different language should be quiet in the church meeting. He should speak only to himself and to God.

You shouldn't stop someone from speaking in tongues.
1 Corinthians 14:39
And do not stop people from using the gift of speaking in different kinds of languages.

​In Acts chapter two the disciples were filled with the Holy Spirit and spoke in other languages. These were definitely known languages because the people who had gathered there heard them in their own language.

Someone told me once that to test if something is true and from God, ask yourself if it gives glory to him. If it doesn't give glory to God, then it's probably not from him. If it doesn't, it's probably not. So, if someone is speaking in tongues, it should meet the criteria above and it should glorify God.