en_tn/jer/06/18.md

Therefore, nations, listen! See, you witnesses, what will happen to them.

These two sentences are telling the people of other nations to witness what Yahweh will do to the rebellious people of Judah. Alternate translation: "Therefore, you people of other nations, listen! You witnesses, see what will happen to my people" (See: rc://en/ta/man/jit/figs-metonymy and rc://en/ta/man/jit/figs-apostrophe)

Therefore, nations, listen!

"Therefore, nations, listen to what I am about to say!"

you witnesses

"you who are witnesses"

will happen to them

The word "them" refers to the people of Israel.