I believe tongues are not only another language but is also our spirit praying to God and also for evidence of having the Holy Ghost (Spirit).
Act 2
1 And when the day of Pentecost was fully come, they were all with one accord in one place.
2 And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting.
3 And there appeared unto them cloven tongues like as of fire, and it sat upon each of them.
4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
5 And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven.
6 Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language.
7 And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans?
8 And how hear we every man in our own tongue, wherein we were born?
9 Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia,
10 Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes,
11 Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God.
12 And they were all amazed, and were in doubt, saying one to another, What meaneth this?
13 Others mocking said, These men are full of new wine.
14 But Peter, standing up with the eleven, lifted up his voice, and said unto them, Ye men of Judaea, and all ye that dwell at Jerusalem, be this known unto you, and hearken to my words:
15 For these are not drunken, as ye suppose, seeing it is but the third hour of the day.
16 But this is that which was spoken by the prophet Joel;
1Corinthians 14
2 For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries.
1Corinthians 14
4 He that speaketh in an unknown tongue edifieth himself; but he that prophesieth edifieth the church.
1Corinthians 14
9 So likewise ye, except ye utter by the tongue words easy to be understood, how shall it be known what is spoken? for ye shall speak into the air.
1Corinthians 14
13 Wherefore let him that speaketh in an unknown tongue pray that he may interpret.
14 For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.
1Corinthians 14
19 Yet in the church I had rather speak five words with my understanding, that by my voice I might teach others also, than ten thousand words in an unknown tongue.
1Corinthians 14
27 If any man speak in an unknown tongue, let it be by two, or at the most by three, and that by course; and let one interpret.
This is talking about an unknown tongue. The unknown tongue is a supernatural language that no one understands but it is that individual's spirit praying to God. However, the fact that this tongue is unknown doesn't take away from the fact that it is also important even though it is less significant than prophesying. It is also stated that one is to pray that they could interpret. The reason why is so that there would be edification in the church.
Apparently there was a lot of tongue talking being used very openly and much emphasis was being put on this particular situation seeing that Paul was admonishing the church on this subject. Even though the word "unknown" was in italics, the fact still was that this tongue was unknow because it by itself was uninterpreted. Paul taught in verse 27 that this tongue should be interpreted. The reason for this was because apparently things were out of order and there needed to be order. If people are assembling together then there is a need for prophesying and the teaching and preaching of God's Word. So Paul told them that there was a need for the unknown tongue to be interpreted so that all may profit from it and so that there would be order.
So I believe that this tongue is words that is not to be understood at first at least. This is why in Acts 2 they said that the men were full of wine - because they couldn't understand what they were saying. Peter then responded by quoting the prophet Joel saying these were the things that were to take place in the last days.
1Corinthians 12
10 To another the working of miracles; to another prophecy; to another discerning of spirits; to another divers kinds of tongues; to another the interpretation of tongues:
1Corinthians 12
30 Have all the gifts of healing? do all speak with tongues? do all interpret?
I believe from studying the Bible there are two different types of tongues and possibly three when the uninterpreted tongue is able to be interpreted through the power of God as a prphetical utterance. These are from the Lord not learned but supernatural:
1. Tongues uttered in a different nationality spoken through the divine influence of the Holy Ghost through an individual that had no prior learning of the particular language (Acts 2).
2. Tongues spoken supernaturally that no one understands but God (1 Corinthians 14:2
. This is the uninterpreted tongue. I believe this tongue was intended to be between the individual and God because it says "no man understands him." However, once again, God can allow a tongue to be interpreted. It all depends upon the grace given of God.
3. The tongues that are interpreted into prophesy (I believe these tongues are specifically designed purposely to be interpreted as prophesy). For an example, if you were praying in tongues at your home God may not have a message for you or anyone else for that matter. This would be mostly for an open congregation for the benefit of the church.
1Corinthians 14
18 I thank my God, I speak with tongues more than ye all:
19 Yet in the church I had rather speak five words with my understanding, that by my voice I might teach others also, than ten thousand words in an unknown tongue.
Here it is very plain even though tongues are not edifying to others except through interpretation, that Paul said he thanked God that he spoke with tongues more than all of them. In verse 19 he also made clear that tongues were not edifying to people who were not believer's.
Even as the 120 were gathered together at the beginning of the birth of the church and at other times in the New Testiment, God is very able all by Himself to fill each believer with the Holy Ghost who have first repented of their sins. Secondly, either before or after receiving the Holy Ghost, they are to be baptized in the Name of the Lord Jesus Christ as was commanded and carried out in God's Word.
1Corinthians 14
21 In the law it is written, With men of other tongues and other lips will I speak unto this people; and yet for all that will they not hear me, saith the Lord (This is quoted from Isaiah 28:11-12).
22 Wherefore tongues are for a sign, not to them that believe, but to them that believe not: but prophesying serveth not for them that believe not, but for them which believe.
I believe what is quoted in verse 22 is talking about tongues being a sign for the one who first receives the gift of the Holy Ghost. Because the subject at hand is addressing problems with tongues being used in the church openly in the congregation. That is why he possibly skipped over the part about it being a "refreshing," because most probably they were over using tongues in particular. Prophesying serves for those that believe. Kept within context, this is talking about the believer prophesying and as I stated earlier, tongues are for the new believer's.
When a person had received the infilling of the Holy Ghost, many times the "sign" was speaking in tongues.
Acts 2
4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance.
Acts 10
46 For they heard them speak with tongues, and magnify God. Then answered Peter,
47 Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?
Act 19
6 And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied.
In Acts Chapter 8 they most probably spoke in tongues seeing that Peter and John came down to pray for them to receive the Holy Ghost and afterwards this sign was so amazing that Simon the sorcerer wanted to buy this gift of laying on of hands from the two apostel's. If they would have received it after only believing that would have proved to be suficient. However, it wasn't seeing that they came down to lay hands on them. It was apparent that there was need of a "sign." This sign many times was very needful so that everyone would know that had indeed received the gift of the Holy Ghost. So there you have it. Biblically this was used for a sign, and Paul himself also saying he spoke in tongues most certainly as well had the same experience after his own personal conversion.
God bless