In accord with the reading of both manuscripts, the 1981 LDS edition restored the correct plural temptations here in Alma 34:39. Elsewhere in the Book of Mormon text, we always have a semantically plural use of temptation when this word is postmodified by a prepositional phrase beginning with of (usually the phrase is “of the devil”):
It seems that the change in Alma 34:39 to “the temptation of the devil” in the 1830 edition was an error (and probably unintentional since the plural is perfectly acceptable).
Summary: Maintain the correct plural temptations in Alma 34:39 (“the temptations of the devil”), the reading of the manuscripts.