Jeff Lindsay notes that the issue of Isaiah variants in the Book of Mormon is a complex and interesting topic now for scholars. They have found support for the Book of Mormon variants in other biblical texts. Franklin Harris writes:
In Isaiah 5:5 (2 Nephi 15:5) the Book of Mormon adds "I will" making the clause read "and I will break down the wall thereof." This reading is precisely that of the Septuagint which renders "and I will pull down its walls." (Franklin S. Harris, Jr., The Book of Mormon: Messages and Evidences, pp. 50-52)
[Quoted by Jeff Lindsay, "Did Joseph Smith Plagiarize from the King James Bible?," Book of Mormon Commentary, [www.jefflindsay.com]]