Allen H. Richardson and David E. Richardson discuss the use of "adieu" in Jacob 7:27.
Allen H. Richardson and David E. Richardson, 1000 Evidences For The Church of Jesus Christ of Latter-day Saints, 2 vols., 2nd ed (South Jordan, UT: Artisan Enterprises, 2003), 2:280
EVIDENCE 936: ADIEU
CLAIM: The closing word in the book of Jacob has been the subject of harsh criticism by faultfinders. However, the fact that Jacob ends his book with the French word adieu (Jacob 7:27), has actually become another evidence for the truthfulness of the Book of Mormon.
EVIDENCE: The word adieu that Joseph Smith employed in the translation of the Book of Mormon, is in fact the best word to convey the original meaning that Jacob had written and therefore strengthens the case for the accuracy of the translation. There are several factors that one should consider in this matter:
1) Those who have for many years asked: “How did a French word get into the writings of a supposedly Hebrew prophet?” might just as well have asked how so many English words got into the Book of Mormon. The obvious fact is that the prophet writers of the Book of Mormon wrote neither French nor English, but Joseph Smith used these words as he translated the meanings of their ancient Hebrew thoughts into words that we could understand. As a translator, Joseph Smith naturally used words that were common to him in his time and locale. It is a matter of history that the New England area where Joseph Smith was born and raised was populated by many French who had migrated down from over the border of French-Canada.
2) Being a composite of several older languages, the English language borrows from many countries especially France. Indeed, many of the words in our English language are actually French. Such English words as faith, repent, and prison originated in the French Language. These and many others appear in the King James Bible.
3) Some uniquely French words also appear in the King James Bible such as tache (Exodus 26:6, 11), laver (Exodus 30:18, 28) and brute (Jeremiah 10:22; Nahum 3:19). Those who criticize the Book of Mormon for using a French word are inadvertently criticizing the Bible, which could be said to be guilty of the same charge.
4) The last written word of the prophet Jacob is most likely a translation of the Hebrew word Lehitra’ot which carries virtually the same meaning as the French word adieu. Both words convey more than a simple farewell—each includes the invocation of a blessing. (See Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon, [1977], p. 163.)