First, the word, "glossalalia" does not appear anywhere in the NT - it is a modern word that simply means "tongues-speaking"; it is a technical term for those denominations that practice speaking in unknown languages.
Second, there is a significant difference of opinion between two branches of Christianity that believe one of two ideas:
- That the "glossa" of Acts 2 and 1 Cor 14 are the same
- That the "glossa" of Acts 2 and 1 Cor 14 are different; specifically that in 1 Cor 14 is discussing (humanly) unknown languages and Acts 2 is discussing known languages.
I will resist the temptation to comment on this matter and concentrate only on the OP's question about whether the phenomenon of Acts 2 indicated known or unknown languages.
Acts 2 - Known or Unknown Languages?
The answer to this question was given some time ago in another question whose accepted answer is reproduced below.
The important point to note here is that Luke is (typically) very careful in the use of his terms when describing what went on at Pentecost. He clearly says that people understood what was said; and more specifically, says that they understood in their own local "dialect". This leaves no room to doubt that what was being said was understood by the hearers.
Now, to what extent the miracle of Pentecost was a miracle of the speakers of the hearers is another matter. Below, I suggest it was some combination of both!
However, for the moment that does not matter. The fact remains that people heard the apostles in their own languages and even their own dialects. Thus, "other tongues/languages" were known human languages in Acts 2.
[NOTE: the Greek word γλῶσσα (glossa), the Latin word lingua, and the English word "tongue" all mean the same thing: either the physical organ of the human body or a human language or language group.]
APPENDIX - Were the "Tongues" of Acts 2 Known or Unknown?
This answer is reproduced from my answer here >> In Acts 2:6, was the miracle in the speaking or the hearing at Pentecost?
The important and critical verse is Acts 2:6 in this passage of v1 - 13.
Acts 2:6 - And when this sound happened, the assembled multitude was
bewildered because they were hearing them speaking, each one, in his
own dialect. (My translation)
But first some background.
Three times in this passage, Luke uses a variant of the same verb, πληρόω (pléroó) in several cognate forms:
- V1, "fulfilled" συμπληροῦσθαι (symplērousthai)
- V2, ""it filled" ἐπλήρωσεν (eplērōsen)
- V4, "were filled" ἐπλήσθησαν (eplēsthēsan)
Three times the Holy Spirit is recorded as performing a remarkable, supernatural miracle on the assembled group of people:
- V3, Tongues of fire "appeared"
- V4, They began to "speak" in other languages
- V6, They were "hearing" - each in his own dialect (and V8)
Note the important word (unique to Luke) in V6 & V8 "dialect" διαλέκτῳ (dialektō) as distinct from the word for "language" γλῶσσα (glóssa) in V4. "Dialect" here is not just the language group but the particular form of the language unique to each area. As Meyer's commentary observes:
διαλέκτῳ is here also not national language, but dialect (see on Acts
1:19), language in its provincial peculiarity.
Thus, while V9-11 lists 16 language groups, there were probably hundreds of provincial dialects - more than the number of disciples preaching at Pentecost.
Now, the important question is this: Is the "gift of tongues" as recorded in Acts 2:1-13 a miracle of the speaker, or the miracle of the hearer, or both? Based on the above evidence, I would suggest it is BOTH. I am sure (based in 1 Cor 14, etc) that the disciples miraculously spoke other languages, see V4, V11. Equally, the hearers then heard the message proclaimed in their own provincial language dialect, V6, V8.
So Luke is quite precise in his terminology here: The speakers spoke other languages while the hearers heard their own dialects. That is, a miracle of both the speakers and the hearers.
There is a similar miracle, performed by the Holy Spirit, recorded in Rom 8:26 where He (the Holy Spirit) translates the language that a Christian petitioner asks of God:
In the same way the Spirit also helps our weakness; for we do not know
how to pray as we should, but the Spirit Himself intercedes for us
with groanings too deep for words;
Thus, the miracle of Pentecost is not unique; nor is it beyond the power of omnipotence.