Is there such thing as an “unknown” prayer language when one talks about speaking in tongues? The King James Version added the word "unknown" several times in 1 Corinthians chapter 14, in an attempt to clarify what was being stated. These additions are marked by the word "unknown" being italicized. The word “unknown” 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 today which have decided that "unknown" must mean unknown to anyone on earth and therefore have declared that Paul was talking about speaking in the tongue of angels. This far from the truth and is easily seen in the text.
The word "tongue" simply refers to a language. We still use it in this sense today, 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. Acts 2:6 KJV “Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language." These visitors in Jerusalem were from at least fifteen regions of the world, but when the apostles spoke each listener heard his own language! This was not an “angelic language”. Paul teaches later 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). Yet, in contrast, prophesy was always beneficial. Paul also 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 has no purpose.
Prayer done in an unknown tongue might benefit the spirit of the one praying, but it doesn't help the praying person if he doesn't understand the language. Notice especially verse 15. 1 Cor. 14:13-15 KJV “Wherefore let him that speaketh in an unknown tongue pray that he may interpret. For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful. What is it then? I will pray with the spirit, and I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also”. This is the opposite of what is being advocated by many churches today which claim miraculously speaking in tongues is still occurring today. Besides, prayer in worship should also benefit the listener. Paul tells the Corinthians to speak so that those listening will understand and gain knowledge from hearing (I Corinthians 14:16-19).
Finally, Paul points out that speaking in tongues was given to reach unbelievers (I Cor. 14:22). Using a language that the unbeliever doesn't understand defeats the purpose for which the gift was given in the first century. Instead of being impressed, the unbeliever will leave thinking everyone is in the congregation is insane (I Cor. 14:23)! Isn't this what happens in most services today where people claim to speak in tongues? People babble, but no one is edified, including the babbler! The speaker might feel uplifted, but he hasn't learned nor taught a thing. I would much rather with sincerity and understanding, than to force myself to speak in an “unknown” and “pretend” language. Ask yourself logically, which will lead people to the knowledge of Christ today? Paul teaches that the miraculous gifts (which include speaking in tongues) will cease “when that which is perfect is come” (1 Cor. 13:10). Many teach that “perfect” thing is Christ and therefore “tongues” will continue until the judgment. However, the word “perfect” means complete. This “complete” thing is mentioned in James 1:25 and is the “perfect law of liberty” which is our completed New Testament. Therefore, not only is “speaking in tongues” not an angelic language, this ability to miraculously speak another language ceased when the Scriptures were completed.