Isaiah 52:8 (King James Bible) thy watchmen shall lift up the voice
In this Isaiah quotation, we have two minor variants in the printed editions. First, the 1888 LDS large-print edition omitted the adverbial up. This omission was undoubtedly accidental since in three other places where this same Isaiah verse is quoted the up is retained in the 1888 edition (see Mosiah 12:22, 3 Nephi 16:18, and 3 Nephi 20:32).
Second, in the 1953 RLDS edition, the singular voice was replaced by the plural voices. This change appears to be intentional since the same change is found in the 1953 edition when this Isaiah passage is paraphrastically quoted later in 3 Nephi:
The apparent motivation for the emendation to voices is the occurrence of their before voice in Mosiah 15:29 and 3 Nephi 20:32 (“lift up their voice” in the earliest text). Note that when Isaiah 52:8 is literally quoted in the Book of Mormon (as “lift up the voice”), the singular voice is maintained in the 1953 RLDS edition as well as in all other printed editions:
(For the variation regarding the number of watchmen in the first example, see the discussion under Mosiah 12:22.) The critical text will maintain the occurrence of the singular voice in both Mosiah 15:29 and 3 Nephi 20:32. Since both of these quotations are somewhat paraphrastic, the their will also be maintained.
Summary: Maintain in Mosiah 15:29 and 3 Nephi 20:32 the phraseology “lift up their voice”, in accord with the reading of the earliest textual sources; the occurrence of their in this phrase appears to be intentional since both these quotations of Isaiah 52:8 are somewhat paraphrastic.