en_tn/isa/11/12.md

He will set up a signal flag for the nations

Possible meanings are 1) "The Lord will set up the king as a signal flag for the nations" or 2) "The king will set up a signal flag for the nations" (See: rc://en/ta/man/jit/figs-metaphor)

a signal flag for the nations

"a flag for the nations to see" or "a flag to call the nations to himself"

signal flag

See how you translated this in Isaiah 5:26.

the dispersed of Judah

"the people of Judah who had been scattered around the world"

from the four corners of the earth

The earth is pictured as if it has four corners, and those corners are its most distant places. This refers to everywhere on earth where those people might be. Alternate translation: "from even the most distant places of the earth" or "from all over the earth" (See: rc://en/ta/man/jit/figs-synecdoche)