I just watched a movie on Prime (most of the movie, anyway) about the centuries-long effort to decipher the Mayan hieroglyphics. They've done a pretty good job of it, but it was really hard. They do not have a Rosetta Stone to work with.
The Minoan language has been likely dead for 2000 years.
That was also the breakthrough with the Rosetta Stone too. That Coptic was a modern version of ancient Egyptian.
fairly watchable.