What do you think of when you read this:
"And when the Day of Pentecost was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing wind, and it filled all the house where they were sitting. And there appeared unot them cloven tongues as of fire, and it sat upon each of them. And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance."
Many people say that this was a special "spirit language" that God used to shock the Jews in Jerusalem to get their attention. They were indeed shocked (v. 7), but by what? Verses 5-11 explain:
"And there were dwelling at Jerusalem Jews, devout men, out of every nation under Heaven. Now when this was noised abroad [how that the disciples spake with other tongues], the multitude came together [to see what the fuss was all about], and were confounded, because that every man heard them speak in his own language. And they were all amazed and marvelled, saying one to another, 'Behold, are not these which speak Galileans? And how hear we every man in our own tongue, wherein we were born? Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judea, and Cappadocia, in Pontus, and in Asia, Phrygia, Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes, Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God.'"
Unlike the common practice today, those around them could easily verify that the words that the disciples uttered belonged to other distinct, identifiable, in-common-use-at-that-time languages. This was not meaningless babbling with mysterious interpretations; this was the use of languages in which the disciples had not been educated, a miracle that none could deny.
And the response of these devout Jews was correct: they did not assume that because it was mysterious that it was from God; they asked what it meant (v. 12). They knew that if it was being used to try to turn them away from worhsipping the One True God, that they would have to stone those who were the instruments of this performance (Deuteronomy 13:1-5). They also knew that if God had indeed raised these men up to preach to them, that they would answer for rejecting their word (Deuteronomy 18:18-19).
Note also, that while they were "speaking in other tongues" the disciples were recounting what the Jews already knew to be "the wonderful works of God": they were not bringing some new revelation. Though the Gospel was as yet unknown to these Jews, yet, when it was time to share it with them, Peter used the common tongue to speak to them all--which they understood from from their Jewish upbringing--which was the only way that they all could understand him at the same time, because they did not know all of each others' languages, which is why they were so surprised to here them coming from the mouths of a company of Galileans. (Galilee was reckoned as the slums.)
Paul, commenting on the gift of tongues in 1 Corinthians 14:18-25, said:
"I thank my God, I speak with tongues more than ye all: Yet in the church I had rather speak five words by my understanding, that by my voice I might teach others also, than ten thousand words in a tongue. Brethren, be not children in understanding: howbeit in malice be ye children, but in understanding, be men.
"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.' Wherefore tongues are for a sign, not to them which believe, but to them which believe not: but prophesying serveth not for them that believe not, but for them which believe.
"If therefore the whole church be come together into one place, and all speak with tongues, and there come in those that are unlearned, or unbelievers, will they not say that ye are mad? But if all prophesy, and there come in one that believeth not, or one unlearned, he is convi[cted] of all, he is judged of all: and thus are the secrets of his heart made manifest; and so falling down on his face he will worship God, and report that God is in you of a truth."
Matthew Henry notes:
"Tongues were rather a sign to unbelievers than to believers. They were a spiritual gift intended for the conviction and conversion of infidels that they might be brought into the Christian church; but converts were built up in Christianity by profitable instructions in their own language. That gifts may be rightly used, it is proper to know the needs which they are intended to serve. To go about the conversion of infidels as the apostles did had been a vain undertaking without the gift of tongues and the discovery of this gift; but in an assembly of Christians already converted to the Christian faith, to make use and ostentation of this gift would be perfectly impertinent because it would be of no advantage to the assembly; not for the conviction of the truth because they had already embraced it; not for their edification because they did not understand and could not get benefit without understanding what they heard.
"The Christian religion is a sober and reasonable thing in itself and should not, by the ministers of it, be made to look wild or senseless. Those disgrace their religion and vilify their own character who do anything that has this aspect. But on the other hand, if instead of speaking whith tongues, those who minister plainly interpret Scripture or preach in language intelligible and proper, the great truths and rules of the Gospel, a heathen or unlearned person coming in will probably be convinced and become a convert to Christianity. Scripture truth plainly and duly taught, has a marvelous aptness to awaken the conscience and touch the heart. And is not this much more for the honor of our religion, than that infidels should conclude the ministers of it a set of madmen, and their religion exercises only fits of frenzy? This last would at once cast contempt on them and their religion too. Religiosu exercises in Christian assemblies should be such as are fit to edify the faithful, and convince, affect, and convert unbelievers. The ministry was not instituted to make ostentation of gifts and parts, but to save souls."
The example which we have is Acts 2, where the disciples spoke in many languages, known to be so, to gain the attention of the unbelieving Jews, and then spoke unto them the Gospel in words which they all understood. They all understood the priests in the Temple, so that is the language in which Peter ministered unto them the Gospel.
I remember a lady telling me about the time in which she was lost in China and had to rely on her knowledge of the native language to get help. She being a white woman, everyone who heard her speak in their language was shocked. If she had been a missionary, what a great testimony to be used to bring about the conversion of the Chinese!