Paul Davidson, on the Recovery from Mormonism discussion board, says a Mormon apologist defending the concept of the LDS teachings about the Book of Mormon  being written in “reformed Egyptian” told him:

“By the ninth to sixth centuries before Christ, Israelites used Egyptian numerals mingled with Hebrew text. The Papyrus Amherst 63 contains a text of Psalms 20:2-6 written in Aramaic (the language of Jesus) using Egyptian characters. This text was originally dated to the second century B.C., but this has since been extended to the 4th century B.C. For further examples you can see the Byblos Syllabic texts, the Cretan hieroglyphics, Meroitic, Psalm 20 in demotic Egyptian (seen above), and Proto-Sinaitic and the alphabet.”

In response, Richard Packham, a linguist, wrote the following. (I have hyperlinked his supporting articles within the text):

It is a well-known fact that a language can (and usually will) be modified by its speakers over the course of several centuries. Critics are quite mistaken to claim that no such thing as “reformed Egyptian” could exist. I discuss this briefly in my article. Everybody overlooks the statement that the first part of the BoM, written by Nephi and his immediate successors, was not written in “reformed Egyptian,” but simply “Egyptian,” before the passage of time necessary for a language to change enough to be called “reformed.” (1 Ne 1:2) Mormon apologists interpret the phrase at 1 Ne 1:2 (“the language of my father, which consists of the learning of the Jews and the language of the Egyptians”) to mean that the language was Hebrew, but written in Egyptian characters. One reason that they insist on this is to bolster their claim that the BoM language reflects many “Hebraisms” – patterns of language peculiar to Hebrew. They reject the counter-argument that Joseph Smith (and any co-authors) were extremely familiar with the language of the King James Bible and naturally used many such linguistic features in producing the BoM.

Iis also a well-known fact that spoken languages can be represented by writing systems (alphabets) other than the customary one, or one borrowed from another culture, and the apologists give several excellent examples.

However, those facts still leave some serious questions unanswered:

WHY would a devout Jewish family write Hebrew in a foreign alphabet? The examples given by the critics of writing one language in the alphabet of another (writing Chinese in Latin characters) are completely non-analogous to the situation of Jews in Lehi's Jerusalem. Those examples are for making it easier for foreigners to pronounce the other language by using a writing system they are familiar with. No Chinese person would write records for his own use using Latin characters. The Yiddish example is also not analogous. The Yiddish-speaking Jews were writing their own language using their own well-known (from synagogue) alphabet.

Even more unbelievable is the statement in the Book of Mormon that Laban kept the Brass Plates records using Egyptian (Mosiah 1:4). Why would such important records be kept in Egyptian? Apologists cannot point to a single instance where important records of the Jewish people in 600 BC, kept for their own use and not for foreigners, were not kept in Hebrew. (See my article on the Brass Plates)

The Papyrus Amherst 63 does not help, since it appears to be a kind of script for liturgical reading, to enable someone who could pronounce Egyptian letters to say the Psalm in Aramaic, without actually knowing any Aramaic. That would not be the situation with Lehi's people.

The reason given in the BoM for using Egyptian was that it was much less space-consuming than Hebrew. This argument fails when one compares the space required to write Egyptian (any form) and the space required to write Hebrew. See my discussion .