Because Luke, who knew Paul, tells us that this is what Jesus said to Paul, I believe it.  Acts is an inspired book!  And Luke is a careful historian. Whether the voice Paul heard was in Aramaic or in Greek, who knows?    Does it matter?   Paul surely spoke Aramaic, Hebrew and also Greek, as he lived in a Greek-speaking city of Tarsus.    Luke did not specify what language Paul heard.   I suppose, most likely, it was the language most familiar to Paul, which was probably Aramaic, or possibly Greek.  You say that God was speaking to Paul in Hebrew?  How does one know that?

What the Lord told Paul here is spoken in the form of a common idiom/proverb.   When we speak an idiom, we are not quoting a person, but the idiom.  For example, when I say “A bird in the hand is worth two in the bush,” I am not quoting someone, but I am using the common proverb that I assume everyone knows.  In fact, I have no idea who said that first.  Maybe it was Benjamin Franklin.  But, when I speak in a proverb, I am not quoting a particular person.

So, no, God is not “quoting” Dionysus!!!   He certainly is not “quoting” Euripedes.   He is speaking to Paul in terms he would understand, using an idiom that Paul would understand.  It seems to me that someone is trying to invent a reason to doubt the Scriptures here, as a common-sense approach tells us that there is no cause for doubt here.

John Oakes