There are two examples in the Book of Mormon text of the plural judgments in the phrase “judge righteous judgments”. The other example occurs later on in this chapter: “and he did judge righteous judgments” (verse 43). But one might wonder if the plural judgments might be an error for the singular judgment because of the corresponding language in the King James Bible: “judge not according to the appearance but judge righteous judgment” (John 7:24). However, the plural “righteous judgments” does occur in the King James Bible (five times in Psalm 119). Further, Revelation 16:7 and 19:2 refer to the judgments of God as true and righteous.
The singular “righteous judgment” does occur in the Book of Mormon; but when it does, it is always preceded by the indefinite article a:
So there is no textual evidence except the familiar usage of John 7:24 to suggest that the two occurrences of the plural “judge righteous judgments” (both here in Mosiah 29) might be wrong.
Summary: Retain the plural judgments in the phrase “judge righteous judgments”, which occurs twice in Mosiah 29 (verses 29 and 43).