Demotic Language and Reformed Egyptian
Another key to Reformed Egyptian wasn't found until decades after the death of Joseph Smith. It is a form of Egyptian language called Demotic. It is a short-hand form of Egyptian, greatly reducing the size and number of strokes required in normal hieroglyphics. The Demotic language was in use during Lehi's time, possibly used more in normal transactions than hieroglyphics.
You can find more on Demotic script and the Oriental Institute's Demotic Dictionary project at:
Oriental Institute's Demotic Page