en_tn_condensed/isa/34/08.md

it will be a day of vengeance for Yahweh

Here "day" is an idiom for a point in time; it is not a literal "day." Alternate translation: "it will be the time when Yahweh gets revenge" (See: rc://en/ta/man/jit/figs-idiom)

he will pay them back for the cause of Zion

This means that he will take revenge on them for how they had previously waged war against the people of Jerusalem. Alternate translation: "he will give them the punishment they deserve for what they had done to the people of Zion" (See: rc://en/ta/man/jit/figs-explicit)