en_tn/2ch/23/21.md

So all the people of the land

This is generalization to say that most of the people rejoiced. (See: rc://en/ta/man/jit/figs-hyperbole)

the city was quiet

Here "the city" represents the people of the city, and "quiet" represents peace, since no one opposed Joash after Athaliah died. Alternate translation: "the people of the city were at peace" (See: rc://en/ta/man/jit/figs-metonymy)