Isaiah 3:8–9 (King James Bible)
for Jerusalem is ruined and Judah is fallen because their tongue and their doings are against the LORD to provoke the eyes of his glory the shew of their countenance doth witness against them and they declare their sin as Sodom they hide it not woe unto their soul for they have rewarded evil unto themselves
Generally speaking, the Book of Mormon text prefers plurals when referring to the eyes, tongues, and hearts of people—or to their souls and minds. Thus here in 2 Nephi 13:8–9, we have tongues and souls rather than the King James (and original Hebrew) singulars. Another example of this difference in number is found near the end of this long Isaiah quotation:
Similarly, each person has one mind, but in plural contexts the Book of Mormon text always uses the plural minds when referring to a group of people, even when these people are “of one mind”:
This particular plural was edited by Joseph Smith to the singular mind, but the change was not implemented in the 1837 edition. For further discussion, see Alma 17:6.
Thus in Book of Mormon biblical quotations, the use of plurals instead of singulars for individual parts of the body and for the spirit or mind seems fully intended. Yet not every instance of an individual characteristic has been changed to the plural in the original Book of Mormon text. For instance, here in 2 Nephi 13:9 the original text has “the shew of their countenance”, although the 1874 RLDS edition changed the singular countenance to the plural countenances (perhaps under the influence of the preceding “their tongues and their doings”). The 1908 RLDS edition (which generally follows the reading of the printer’s manuscript) restored the original singular countenance, the reading of the King James text.
Summary: Retain the plural tongues and souls in 2 Nephi 13:8–9 and the singular countenance in 2 Nephi 13:9.