The gift of interpretation of tongues is a very important gift according to 1 Corinthians 14. It enables the person with the gift to understand and interpret what someone with the gift of tongues is saying, so that the church may be edified by the content of the message.
1 Cor 14:1-5 (ESV):
Pursue love, and earnestly desire the spiritual gifts, especially that you may prophesy. 2 For one who speaks in a tongue speaks not to men but to God; for no one understands him, but he utters mysteries in the Spirit. 3 On the other hand, the one who prophesies speaks to people for their upbuilding and encouragement and consolation. 4 The one who speaks in a tongue builds up himself, but the one who prophesies builds up the church. 5 Now I want you all to speak in tongues, but even more to prophesy. The one who prophesies is greater than the one who speaks in tongues, unless someone interprets, so that the church may be built up.
1 Cor 14:13 (ESV):
13 Therefore, one who speaks in a tongue should pray that he may interpret. 14 For if I pray in a tongue, my spirit prays but my mind is unfruitful.
1 Cor 14:26-28 (ESV):
26 What then, brothers? When you come together, each one has a hymn, a lesson, a revelation, a tongue, or an interpretation. Let all things be done for building up. 27 If any speak in a tongue, let there be only two or at most three, and each in turn, and let someone interpret. 28 But if there is no one to interpret, let each of them keep silent in church and speak to himself and to God.
After reading 1 Corinthians 14, one can easily get the impression that, without someone with the gift of interpretation of tongues at hand, tongues should be entirely avoided in public settings and reserved for private use only. Which makes a lot of sense, until we bring Acts 2 into the picture:
Acts 2:1-13 (ESV):
When the day of Pentecost arrived, they were all together in one place. 2 And suddenly there came from heaven a sound like a mighty rushing wind, and it filled the entire house where they were sitting. 3 And divided tongues as of fire appeared to them and rested on each one of them. 4 And they were all filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance.
5 Now there were dwelling in Jerusalem Jews, devout men from every nation under heaven. 6 And at this sound the multitude came together, and they were bewildered, because each one was hearing them speak in his own language. 7 And they were amazed and astonished, saying, “Are not all these who are speaking Galileans? 8 And how is it that we hear, each of us in his own native language? 9 Parthians and Medes and Elamites and residents of Mesopotamia, Judea and Cappadocia, Pontus and Asia, 10 Phrygia and Pamphylia, Egypt and the parts of Libya belonging to Cyrene, and visitors from Rome, 11 both Jews and proselytes, Cretans and Arabians—we hear them telling in our own tongues the mighty works of God.” 12 And all were amazed and perplexed, saying to one another, “What does this mean?” 13 But others mocking said, “They are filled with new wine.”
If having people around with the gift of interpretation of tongues is of paramount importance when tongue speaking in public settings, then how come that in Acts 2 there was no need for interpreters? Were tongues in Acts 2 in some sense special? How can we determine when interpreters are necessary and when they aren't?