Abraham, living in Ur, would have spoken old Akkadian, which replaced Sumerian in Mesopotamia.
Sumerian is the oldest written language in the world.
Coptic Egyptian (essentially the language of the people who built the pyramids) is the oldest surviving spoken language in the world. It's still used as a liturgical language by Coptic Christians.
The people who built Gobekli Tepe in Turkey, obviously had some language long before Egyptian or Sumerian, but they left no writing that might have let us know what it was like.