Criticism: There is no such language as "Reformed Egyptian".
Response: Reformed egyptian isn't a language. It's a system of writing. There were three basic forms of Egyptian writing: the original hieroglyphic, a Greek variant that developed later called hieratic, and a third form in use around 700 BC called demotic. The latter two represent a shorthand form of hieroglyphic, each symbol standing for a concept rather than a lone consonant or vowel, allowing a scribe to compress a large amount of ideas into a small space. For more background on these systems of writing relative to Book of Mormon scholarship, study Two Notes on Egyptian Script by John Gee and Jewish and Other Semitic Texts Written in Egyptian Characters by Stephen D. Ricks, and John A. Tvedtnes.
Just like I can go to this web site, type in any word, phrase, or sentence, and get its approximate phonetic spelling in Egyptian hieroglyphics, if I had a similar decoding/encoding system for Reformed Egyptian, I could do the very same thing with translating Hebrew sounds and concepts to a hieratic or (more likely) a demotic writing form.
Is it Joseph Smith's lucky guess that such a writing system would be perfect for engraving a book as large as the Book of Mormon onto plates of metal that would be difficult to produce, carry, and preserve, in large quantities as opposed to "longhand" script like Hebrew?