As is commonly known, the Rosetta stone provided the key to solving the mystery of hieroglyphics. Was there a comparable key for Cuneiform? When was it first deciphered?
Hi! If there a specific language you're wondering about, I might be able to find more info (and of course I'm not discouraging anyone else from answering here). Meanwhile, these earlier posts might provide a useful starting place:
When and how were cuneiform languages (like Akkadian and Sumerian) first deciphered by modern scholars? - /u/Wedgehead discusses the Behistun Inscription, which was written in Old Persian, Akkadian, and Elamite; and Sumerian.
If Sumerian is a language isolate, how was it deciphered? - /u/farquier on Sumerian
Not quite on topic, but of possibly tangential interest