The Standard Babylonian Epic of Gilgamesh is written in Akkadian. Akkadian was a Semitic language recorded in cuneiform and used widely in ancient Mesopotamia for administration, scholarship, and literature.
The poem’s Standard Babylonian form is generally dated to the second millennium BCE, although its stories originated in earlier Sumerian poems. This version is associated with the Babylonian literary tradition and is the form most often translated and studied today.
A common mix-up is calling the entire Epic of Gilgamesh a Sumerian composition. Several early Gilgamesh stories were written in Sumerian, but the famous long epic was composed in Akkadian. Sumerian and Akkadian were different languages, even though both were written with cuneiform signs.
The best-known surviving copies come from the library of Ashurbanipal at Nineveh. They preserve the Standard Babylonian literary version, including the flood narrative on Tablet XI.