Who knew how to write in hieroglyphs?

Until the Rosetta Stone was uncovered we had no idea what the glyphs meant. When the Rosetta Stone was found we were able to translate because the message was written in more than 1 language. We were able to look at a language we could translate, figure out what was said, then apply a method similar to the cryptographs found in the Sunday paper to the glyphs to figure out how they were drawn.