Grant H. Palmer argues that "raca" would not make sense to the Nephites; the phrase in Matthew 5:41 found in 3 Nephi 12:41 refers to a Roman Law unknown to Book of Mormon peoples.
Grant H. Palmer, An Insider’s View of Mormon Origins (Salt Lake City: Signature Books, 2003), 89-90
What is obvious about this section of the Book o Mormon is that it was borrowed from the KJV and placed in an ancient American context. In some cases, there are still rough edges. Jesus uses the Nephite monetary term “senine” rather than “farthing” (3 Ne. 12:26/Matt. 5:26) and omits references to “scribes and Pharisees” (3 Ne. 12:20/Matt. 5:20) and to swearing oaths “by Jerusalem” (3 Ne. 12:35/Matt. 5:35). But the Book of Mormon retains references to “raca” and to being “in danger of the council” (3 Ne. 12:22/Matt. 5:22): “Whosoever shall say to his brother, Raca [a curse and term of hatred], shall be in danger of the council.” Committing “raca” in Palestine resulted in bring brought before the Jewish Sanhedrin or “council.” As an Aramaic word, “raca” would not have been intelligible to a Nephite.
Jesus also told the Nephites, “Whosoever shall compel thee to go a mile, go with him twain.” This refers to the Roman law that required a slave to carry a burden one mile when asked by a Roman citizen. It would presumably have had no meaning in the New World (3 Ne. 12:41/Matt. 5:41).