We are told the Egyptian they used was Reformed Egyptian, a language so rare that nobody has ever heard of it; no trace has ever been found in any archeological dig anywhere in the world; outside of Mormonism, it simply does not exist!
The Bible was written in the language of the people. The Old Testament was given to God's covenant people, the Jews, and it was given in the Jewish language, Hebrew. The New testament was given in the language of the day, Greek, (and a little Aramaic). In all cases the people for whom it was intended could read and understand. Yet we find that Reformed Egyptian is an unknown language (Mormon 9:34).
It might be argued by a Mormon that it was not unknown to the Nephite people. It should however be remembered - outside of the Book of Mormon, even these Nephite people are unknown, so you have a circular arguement, a real "Catch 22" situation.
If these Nephite people really had existed, and recorded their scriptures in Reformed Egyptian, why has God allowed all trace of them and their language to disappear from the earth?
In answer to the charge that he had used a Greek word in the Book of Mormon Joseph Smith wrote a letter dated May 15 1843 in which he stated:
"There was no Greek or Latin upon the plates from which I, through the grace of God, translated the Book of Mormon."
However, throughout the Book of Mormon we find the use of many Greek words. Alpha and Omega are Greek, so is Synagogue and baptize.
The Book of Mormon also mentions sanctuaries, which is Latin. (See 2 Nephi 28:13; Alma 15:17; 21:6.)
The name 'Jesus' is Greek**. If a nation called Nephites, who were descended from Jewish ancestors had existed, they would have used the name 'Yeshua' which is the Hebrew name.
The word Will implies a future event. It means: Determination; Intention or Resolve.
The word Build means: Begin; Establish; Inaugurate; Originate; Set up; Start.
When the Lord said "I will build" He meant He was going to begin His Church. Yet throughout the Book of Mormon we read of the church existing in America - hundreds of years before Christ. Furthermore, the use of the word "Church" is a problem because it is an Anglo-Saxon word and did not exist when the supposed Book of Mormon plates were being engraved.
When speaking to His disciples the Lord did not use the word 'Church'. That is the English translation of what the Lord said. The Greek word, which in the Bible is translated as church, is ekklhsia. It means 'called out', Christ was about to 'call-out' from the world a people for Himself.
Matthew 16:18 is the first time the word 'church' appears in the Bible - as you would expect - just when Jesus announces His intention to build it. It never existed before; not in Jerusalem and not in America.
**See 2 Nephi 33:6 where Jesus is mentioned 500 (plus) years BC. and is spoken of in the past tense. ("He hath redeemed my soul from hell.")