Would you discuss the idea of praying in a heavenly language where the person is edified even though others don't know what they are saying?
The mention of the language of angels is only found in I Corinthians 13:1 where Paul states that speaking in any language is without benefit if it is not accompanied by love. The passage to which you allude, though, is found in I Corinthians 14. The King James Version added the word "unknown" several times in this chapter in an attempt to clarify what was being stated. The addition is marked by the word "unknown" being in italics. It is not in the original Greek, but the translators of the King James Version felt that it would clarify what Paul was saying. Unfortunately, there are groups who have decided that "unknown" must mean unknown to anyone on earth and have declared that Paul was talking about speaking in the tongue of angels. The truth is far from this and is clearly seen in the text.
First, we must understand that the word "tongue" simply refers to a language. We still use it in this sense in American English when we refer to a person's mother tongue. The proper definition is clearly seen in Acts 2:6 where the first occurrence of tongue speaking is found. "And when this sound occurred, the multitude came together, and were confused, because everyone heard them speak in his own language." People from at least fifteen regions of the world were present, but when the apostles spoke they did not use the local dialect by the native languages of the listeners. An amazing feat for poor fishermen from the backwaters of Galilee.
Paul argues in I Corinthians 14 that prophesy is better than speaking in other languages because there are times when the language spoken is unknown to the audience. When this happens, God understands, but no one else benefits (I Corinthians 14:1-5). In contrast, prophecy is always beneficial.
Paul then argues that speaking in tongues is without benefit if it doesn't have a purpose, such as to teach another. Speaking in another language for that reason alone is just showiness. Speaking in another language without purpose is like playing an instrument without a tune. (I Corinthians 14:6-12)
Prayer done in a tongue might benefit the spirit of the one praying, but it doesn't help even that one person if he doesn't understand the language. Notice especially verse 15, "What is the conclusion then? I will pray with the spirit, and I will also pray with the understanding. I will sing with the spirit, and I will also sing with the understanding." Paul is saying, if you are going to pray, pray so that both your spirit and mind benefits -- in other words, Paul is stating you should pray in a known tongue. (I Corinthians 14:13-15). This is the opposite of what was being advocated by charismatics.
Besides, prayer in worship should also benefit the listener. Paul is telling the Corinthians to speak so that those listening will understand and gain knowledge from hearing you (I Corinthians 14:16-19)
Finally, Paul points out that speaking in tongues was given to reach the unbelievers (I Corinthians 14:22). Using a language that the unbeliever doesn't understand defeats the purpose for which the gift was given. Instead of being impressed, the unbeliever will leave thinking everyone is touched in the head (I Corinthians 14:23).
Isn't this what happens in most charismatic services today? People babble, but no one is edified, including the babbler! Oh, he might feel uplifted, but he hasn't learned a thing. I would rather pray with the spirit in sincerity and pray with my mind in understanding than play the part of a babbling idiot. Which will lead people to the knowledge of Christ?