Isaiah 50:2 (King James Bible)
I make the rivers a wilderness their fish stinketh because there is no water and dieth for thirst
The original dieth in the Book of Mormon text actually agrees with the King James reading. The Book of Mormon quotation introduces a simpler text but also the plural subject they, which requires die rather than dieth according to “standard” Early Modern English (which restricts the use of the inflectional ending -(e)th to the third person singular present).
One should note that the corresponding King James text has “their fish stinketh” rather than “their fish stink”; of course, the subject for the conjoined dieth is also “their fish”. Both these uses of the ending -eth imply that fish is grammatically singular and not plural, as indeed it is in the Hebrew (where fish is feminine singular, although semantically it is used as a collective plural).
In any event, Oliver Cowdery emended the printer’s manuscript to read die (by crossing out dieth and supralinearly inserting die). Oliver’s emendation is clearly a conscious decision since the ink flow is definitely heavier than all the rest of Oliver’s scribal corrections on this manuscript page (page 60 of 𝓟). For further discussion of this kind of editing, see under infl tion endings in volume 3.
Incidentally, when this same verse is cited in the current LDS Doctrine and Covenants, the two -eth endings are removed (the original 1835 edition had stinketh and dieth):
Also note that here in the Doctrine and Covenants, we have “the rivers” rather than “their rivers”; see the discussion above regarding “I make the rivers a wilderness”.
Summary: Maintain the nonstandard use of -(e)th in 2 Nephi 7:2 (“and they dieth because of thirst”); 𝓞 as well as 𝓟 originally read dieth, in agreement with the King James Bible’s “their fish stinketh ... and dieth for thirst”.