en_tn_condensed/isa/27/13.md

a great trumpet will be blown

This can be stated in active form. AT: "someone will blow a trumpet loudly" (See: rc://en/ta/man/translate/figs-activepassive)

the perishing ones in the land of Assyria will come, and the outcasts in the land of Egypt

The understood information can be stated clearly. AT: "those who are in exile and dying in the land of Assyria and the land of Egypt will return to the land of Israel" (See: rc://en/ta/man/translate/figs-ellipsis)

holy mountain

The "holy mountain" is Mount Zion, in Jerusalem. See how you translated this in Isaiah 11:9.