"Zion" is the same as "Jerusalem." The prophet speaks of the city as if it is a daughter. Possible meanings are 1) Zechariah personifies the city as a person who can sing. Alternate translation: "Sing for joy, Zion" or 2) the phrase "daughter of Zion" is a metonym for the people who live in the city. Alternate translation: "Sing for joy, people of Zion" (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-personification]] and [[rc://en/ta/man/jit/figs-metonymy]])
Yahweh speaks of himself by name to express the certainty of what he is declaring. See how you translated this in [Zechariah 1:4](../01/04.md). Alternate translation: "this is what Yahweh has declared" or "this is what I, Yahweh, have declared" (See: [[rc://en/ta/man/jit/figs-123person]])