His one language, Sumerian, was spoken by everyone until the Tower of Babel (after the flood) when God had to confuse their pagan design.
Already in Adam’s lifetime, false religions were taking root.
Erech, now called Uruk, which dates back to approximately 3500 B.C., sported a pagan temple/ziggurat dedicated to Inanna (first female goddess).
Adam and Even probably lived, or at least visited, in this city, and the murder of Abel by Cain may well have been inspired by his worship of Inanna at this very shrine.
Babel was nothing but a larger version of this kind of temple tower used to promote a false god and to seduce the people with sex orgies and crude celebrations designed by the mighty rebel Nimrod (called Gilgamesh in Sumerian history and folklore).