1100 glossa the tongue, a language, and miraculously spoke in other actual languages, i.e. that they could not speak before
Acts 2:3 And there appeared unto them cloven tongues like as of fire, and it sat upon each of them.
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 2:5 And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven.
Acts 2:6 Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language.
Acts 2:7 And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans?
Acts 2:8 And how hear we every man in our own tongue, wherein we were born?
Acts 2:9 Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia,
Acts 2:10 Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes,
Acts 2:11 Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God.
Many people believe speaking in tongues in an "unknown" language. But even on the Day of Pentecost it was known to everyone.