There is no "gift of tongues" in Acts - that gift expects an interpreter (see 1Cor 14), and no such interpreter/interpretation is found in Acts.
1Cor 14 introduces the gift of tongues, which is assuredly NOT a (currently) known language and might often be an angelic language.
For your 1st point, Acts 2:5-11 made that clear
5 And there were dwelling at Jerusalem Jews, devout men,
out of every nation under heaven.
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.
7 And they were all amazed and marvelled, saying one to another, Behold, are not all these which speak Galilaeans?
8
And how hear we every man in our own tongue, wherein we were born?
9 Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia,
10 Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes,
11 Cretes and Arabians,
we do hear them speak in our tongues the wonderful works of God.
This passage is a very clear scripture telling us that tongues are a known foreign language. We have the actual interpreters of those languages in the form of "Jews from every nation under heaven" in vs 5.
As for for your 2nd point about 1 Cor 14
, Paul used Isaiah 28:11 in his 1 Cor 14:21-22
21
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.
22
Wherefore tongues are for a sign, not to them that believe, but to them that believe not: but prophesying serveth not for them that believe not, but for them which believe.
If you are aware of the context of Isa 28, the Israelites (the northern kingdom) were so hard-hearted and stubborn in breaching their covenant with God that God sent a judgment upon them (the Assyrian nation – who spoke in the Akkadian language – a foreign language that Israel would not have known) by bringing them into Assyrian captivity.
The northern kingdom of Israel rejected the rest and the covenant relationship from God, hence, God speak to them in foreign tongues.
The causality is hence
If you reject the rest, then God will speak to you in foreign tongues (the Assyrian language of Akkadian).
So tongues in 1 Cor 14:21-22, from context, also refers to known foreign languages.
I do understand that when Paul gave instructions for tongue speaking in 1 Cor 14, some passages may be unclear in the sense that Paul
could be referring to a heavenly language, especially in verses like
2 For he that speaketh in an unknown tongue speaketh not unto men, but unto God: for no man understandeth him; howbeit in the spirit he speaketh mysteries.
4 He that speaketh in an unknown tongue edifieth himself; but he that prophesieth edifieth the church.
14 For if I pray in an unknown tongue, my spirit prayeth, but my understanding is unfruitful.
These could be taken to imply Paul was actually referring to tongues as a heavenly language.
So the principle is "Use clear scripture of tongues to understand those unclear passages regarding tongues".
The first time tongues were mention, whether in the OT, or in Acts 2 and Acts 10, were actual foreign languages.
So if that is the clear scripture on tongues, when we come to the unclear teachings, say in 1 Cor 14, unless there is clear scripture that tells us that Paul is referring to heavenly languages, we use that principle to guide us in our understanding there.