The thing today called "tongues" is not a language of some people here on Earth as it was at Pentecost. Are today's tongues biblical?
In the Greek, the word translated as tongues is γλῶσσα, glōssa, meaning the literal tongue or a language. When the gift of tongues (speaking in foreign languages) was first given at Pentecost, we know these languages were definitely understood by foreigners. Act 2:7-8, 11 (NIV), “Utterly amazed, they asked: ‘Aren’t all these who are speaking [...]