3 Answers

According to the Bible; everyone spoke the same language until Man decided to build the Tower of Babel. The Lord saw this as a potential object of worship and stopped it by making everyone speak in
different tongues so they could not communicate to finish the building of the Tower. People divided into groups with the ones they could understand. Each group went on to become separate nations...
a little far fetched I know, but it goes along with rest of the Bible stories.

Good question. I am no Bible expert, but I would say that, if you assume that "Adam" equals the idea "first human being", he (they) might have spoken one language which later, as human population spread all over the globe, split up into different linguistic groups.

My guess.

Sorry Adam who?