Whatever language God chose to converse with Adam. Perhaps what came to be known as Hebrew, but there is no way to know.
Perhaps your concern is to the historicity of this claim. There is no reason to believe that this did not happen, except, of course, to deny the historicity of the Book of Genesis. You are certainly welcome to do so, but no less an authority than Jesus attested to the historicity, not only of Genesis, but of Adam himself.
More recently I discovered that the Saami (Laplanders), who had little contact with anyone outside their own circles of reindeer chasers until about 1000 years ago, left cliff and cave drawings which can be "dated" back before the existence of Hebrews or any of the Semitic languages.
Some folks think these guys were in place fishing out of the Arctic Ocean as long as 10,000 years ago (although none of their drawings date that old), and possibly were there during the last big glaciation.
The ancient cliff drawings are representations of various "stories". There are some "husband selecting" stories that are much more in line the tale of Lot and his daughters than just about anything else you can think of.
It's pretty easy to find these things on the internet if anyone has an interest.
If "Adam" is Biblically clocked as preceeding "Lot" and we can postulate that the Biblical chronologies are spiritually correct, it is possible the "flood" being discussed occurred at the end of the last Ice Age (14000 years ago) and not at the time of the flooding of the Black Sea basin (a mere 7500 years ago).
The story of Adam being driven out of Eden (and barred from that place by an angel bearing a flaming sword) would also preceed the desertification of the Sahara, and the last previous desertification would be some time during the last glaciation.
Thor Hyerdahl and other ethnologists proposed that the stories of "Bifrost Giants" current in ancient Norwegian tales probably arose during the last Ice Age, thereby demonstrating that a rollicking good story has a long shelf-life!
‘There is no reason to believe that this did not happen, except, of course, to deny the historicity of the Book of Genesis’
since Genesis delivers up two differing accounts of the Creation, skepticism is certainly on the table concerning its historicity...