language: the spoken tongue of a particular nation or people
This word means "a language", the actual spoken tongue of a nation or ethnic group. It appears only in Acts, and every time it points to a real human language that a real group of people speaks. Luke uses it interchangeably with the more common Greek word for tongue or language (γλῶσσα), and standard reference works line up behind that plain sense.
At Pentecost the crowd hears the disciples speaking, as the text puts it, "each in his own language", and the list of nations that follows (Parthians, Medes, Elamites, and the rest) shows these are known, distinct national languages, not a vague manner of speaking. Scholars still argue about what actually happened at Pentecost:
- whether the disciples miraculously spoke unlearned foreign languages
- whether Luke is composing a reversal of the tower of Babel
- whether the languages involved were only the everyday Aramaic and Greek the disciples already knew
But that debate is about the event, not about this word: the word plainly means "real languages".
Three times the word appears in the phrase translated "in the Hebrew language", describing how Paul addresses the Jerusalem crowd and how the voice from heaven addresses Paul. Here too the word simply means "language". What scholars dispute is the meaning of the accompanying word "Hebrew": most take it to mean "the everyday Aramaic of first century Jerusalem", while a growing minority argue it means "Hebrew proper, the sacred language". Again, that question rides on the other word in the phrase, not on this one.
A note on the English word "dialect", which comes straight from this Greek word: in modern English a dialect is a regional or social sub-variety ranked beneath a standard language, but the Greek word carried no such ranking. In the Greek of the New Testament era it was simply the word for "a people's language", the way writers like Josephus and Philo used it.