Assuming that the Deuteronomic passage does refer to a type of crucifixion suggests that Jacob can discuss it without translation because it was known in his cultural background, since it is usually suggested that Deuteronomy is written as part of the Josian reforms. Of course it may have been translated as crucifixion without any explanation because it was also familiar to Joseph Smith. I tend to see the inclusion of the specific word “crucifixion” as a modern artifact rather than an accurate rendition of the plate text. Even assuming that Jacob understood exactly what crucifixion was, the chance that his audience would be familiar with that form of execution is extremely remote. Those who came from the Old World might possibly know it, but the New World portions of the Nephite population (which would have been significantly larger in number) would not.