Tongues are a sign. In each case in Acts, they signified something beyond themselves. The first sign signified Jesus’ ascension to God’s throne (Acts 2:33). The second sign signified God’s acceptance of Samaritans (compare John 4:9 to Acts 8:14-16), and also signified their own unique apostolic authority to the new converts (Acts 8:18). The third sign signified Gentile salvation to the Jewish church (Acts 11:18). The fourth sign signified Paul’s true apostleship (compare Acts 8:18 to 19:6).
It is not quite true that “Pentecost happened only once”, as some teach. Yes, obviously the original event was never precisely repeated, as there are too many differing variables in each case. But on the other hand, Peter’s point about why they should baptize Cornelius rests on the sameness between Pentecost and Caesarea (Acts 10:47, 11:17).
The book of Acts also describes many other true stories in which people believed in Christ, were water-baptized, and there is no evidence they all (or ever) spoke in tongues. Converts are always water-baptized, but there’s no evidence they all spoke in tongues. There were only twelve original apostles, plus Paul and Barnabas, and they couldn’t be everywhere to lay hands on every new believer. That would have been physically impossible.
None of the epistles teach that a one-time tongues manifestation is always how the Spirit’s filling shows itself, and Acts doesn’t teach this either. The promise was of the Spirit Himself (Acts 2:39), not of His gifts, which He distributes as He pleases (1 Cor. 12:11). God gave tongues in Acts as a sign for distinct historical needs and circumstances unique to those moments, and they were tied to God’s unfolding plan of world redemption.
The local, congregational gift of tongues seems to be different from the language miracles in Acts, even though the word glossa is used in both books. Acts tongues required no interpretation (Acts 2:8), but the church gift of tongues did (1 Cor. 14:11). The unbelievers in Acts 2 all knew the languages, but the hypothetical visitors in 1 Cor. 14:23 would think the speakers were insane.
In three out of four cases in Acts, tongues were a sign to believers. Paul says the tongues in 1st Corinthians 14 were a sign to unbelievers (14:22). In Acts, the female disciples publicly prayed in tongues, but 1 Cor. 14:34 says they should not speak in the church. Because of these differences, it seems correct to speak of the sign of tongues in Acts, and the NT gift of tongues in 1 Corinthians, and that they were different.
Let’s summarize what 1 Corinthians 12-14 says about the gift of tongues.
The power to pray in tongues, and to interpret them, comes from the Holy Spirit (1 Cor. 12:10), as He wills (11). This means the gift cannot be taught or learned. The gift of tongues does not signify membership in Christ’s body (11:12-16), hence, it does not signify salvation. God does not give tongues to every Christian (11:30). It is a less important gift than prophecy (11:31, 14:1).
Someday, tongues will completely stop. Right now, we only see the Lord Jesus Christ in the mirror of Scripture, dimly, due to our feebleness of mind (13:12; see 2 Cor. 3:18 and Jas. 1:23 for “mirror” as a metaphor for Scripture). So, God supplements our weakness with spiritual gifts. But, when the day comes we see Christ face-to-face (1 Jn. 3:2), all these intermediary modes of knowledge will be dropped. We won’t need them, because we will be able to talk to Christ in person
“Face to face” means “in person”, 2 Jn. 12, 3 Jn. 14. The "perfect" in 1 Cor. 13 is clearly not the Scripture, since we have the completed Bible but we still only see dimly.
Spiritual gifts are good things (14:1). Paul was entirely pro-tongues (14:5a), and he says he prayed in tongues a great deal (14:18). He didn’t want tongues forbidden, in spite of the possibility of fraud or abuses (14:39b). Tongues are a prayer (14:2).
No one naturally can understand a tongue; it’s content is a mystery (14:2,9). Not even the speaker understands his own prayer, since he needs to pray for the ability to interpret (13). This is why the language-prayer’s mind is “unfruitful” (14:14). He himself does not grow from praying in a tongue, because he doesn’t understand what he’s saying. The pray-er edifies no one (14:6) until it is understandable (14:6, 13). In fact, not only do tongues not edify, but a whole church all praying in tongues would sound like crazy people (14:23).
Our highest priority in the use of spiritual gifts should be to build up others (14:12). Exalting the gift of tongues, not caring about the health of Christ’s body, and praying audibly in uninterpreted tongues, is childish, carnal behavior (14:20). The gift of tongues wasn’t even given mainly for the church. God usually gives a gift of tongues as a miraculous sign to non-Christians (14:22), whereas prophecy is the gift for the church (14:22, 24-25).
If the gift of tongues manifests in the meeting, no more than a maximum of three people are allowed to pray out loud, and they have to pray one at a time (14:27). If the church doesn’t have anyone with the gift of interpretation, they must be silent (14:28). No one is allowed to claim they couldn’t control themselves, because the Holy Spirit never does that (14:32-33). The Spirit of God, who brought order to the world, does not cause disorder (14:40).
A great many, probably most, charismatic churches break many of the Lord’s rules about tongues. They exalt tongues to a high level of importance. People pray or sing in tongues (or what they call tongues), all at the same time. Women pray tongues in the meeting. People pray and sing without any interpretation. People try to teach others to speak in tongues. There is almost always a spirit of wildness in these meetings All these are sinful.
On the other hand, our non-charismatic churches need to be careful not to squash the Holy Spirit’s fire (1 Th. 5:19-20). The doctrinal errors, leadership scandals, and bizarre behavior we see in many charismatic churches are bad, but they don’t justify fear toward the Holy Spirit Himself. He isn’t false, or bizarre, or wild! Satan would like us to confusedly oppose the Holy Spirit in the name of opposing charismatic disorder.
We can’t determine Bible doctrine by anecdotes. One missionary tells a story about someone in another country coming to Christ because they heard a prayer in their own language. Another missionary tells a story about a demon-possessed person speaking uncontrollably in a tongue. The second story doesn’t prove there are no true tongue manifestations. The first story needs to be tested. Neither story proves anything, doctrinally speaking.
The most credible tongues testimony I’ve heard came from an older believer who listened to a man pray in an unknown language during a meeting. My friend somehow knew what the man was praying. Then, a second man came up to the believer, described what he heard in the prayer, and it was the same (intelligible) words that the first believer heard. So, in other words, God supplied the two brothers with verification. This was first-hand testimony to me, not a hand-me-down fable with questionable or unknown provenance, and related by a Christian man I personally know well.
In summary, I believe the book of Acts describes signs of tongues (intelligible languages), which God gave to verify what He was doing at key points in early church history. 1st Corinthians describes the gift of tongues (unintelligible languages), defines why God gives it, and limits its use. A true gift of language is neither extremely important, contrary to Pentecostalism; but if it's real, then it's a blessing.
 Phillip was not able to do this.
 If the speaker knew what he was saying, he wouldn’t need to pray to interpret.