Reformed Egyptian. Hebrews from Jerusalem did not speak or write in Egyptian, let alone a ‘reformed’ version of it. They spoke and wrote (if they could actually write) in Hebrew.
Mormon 9:32. And now, behold, we have written this record according to our knowledge, in the characters which are called among us the reformed Egyptian, being handed down and altered by us, according to our manner of speech.
Mosiah 1:4 confirms the Brass Plates of Laban were written in a form of Egyptian. Lehi and his family supposedly left Jerusalem c. 600 BCE. Only a handful of people could read or write at that time, let alone in two or more languages (Hebrew, Egyptian – and a ‘reformed’ Egyptian – that no one would understand, then or now). Much of the Bible as we now know it was written later than this and yet the Brass Plates of Laban supposedly contained everything in the Bible up to Lehi’s time. Never mind the fact that much of it had yet to be invented and much later written in the format that ended up matching the KJV in the Book of Mormon. I was going to summarise the problems but discovered that my friend, Richard Packham, had already done a wonderful job of covering all the surrounding problems. This is the link to Richard’s “Problems With the Brass Plates of Laban.” Take a look.