en_tn/isa/25/12.md

The stronghold of your fortress walls he will bring down, he will abase, he will cause to fall

This speaks of Yahweh causing armies to bring down the walls as if he himself were going to bring them down. To "abase" the "wall" is a metonym for humiliating the Moabites by destroying the walls they were proud of. Alternate translation: "He will send an army to humiliate you by bringing down the stronghold of your fortress walls and making them fall" (See: rc://en/ta/man/jit/figs-metonymy)

your fortress

Here "your" refers to the people of Moab. It can be stated in third person to be consistent with the previous verse. Alternate translation: "their fortress" (See: rc://en/ta/man/jit/figs-123person)

bring down ... abase

See how you translated similar words in Isaiah 2:11.