"We" refers to Isaiah and includes the people of Judah. And the words "Moab's" and "his" refer to the people of Moab. AT: "We have heard that the people of Moab are proud and arrogant, and they boast and are full of rage." (See: [[rc://en/ta/man/translate/figs-inclusive]] and [[rc://en/ta/man/translate/figs-metonymy]])
cakes of Kir Hareseth that was completely devastated** - "You will mourn because Kir Hareseth is ruined and you can no longer go there to buy cakes made from raisins." Here "you" refers to the people of Moab. And, "Kir Hareseth" is the name of a city. (See: [[rc://en/ta/man/translate/translate-names]])