The very first Languagehat post was about the language spoken by Adam and Eve, or rather theories thereof, so my eye was lured by a book by Maurice Olender called The Languages of Paradise on that very subject. I managed not to buy it (I’m trying to cut back, honest), but I found an article (pdf file) by Olender from a post on crank linguistics by Cinderella Bloggerfeller, who seems to know a lot about language, so you can find the story (or his version of it) there. If scholarly wackiness amuses you, you’ll enjoy it.
I don’t know what language was spoken by Adam & Eve, or the seven generations that followed them. But the language spoken by the Watchers/Fallen Angels/Sons of God/Nephilim/The Giant rulers/Rakshas (Cf.Gen 6.1)is most likely, “Ancient Tamil”.
I certainly hope you’re kidding!