Following are a number of back-translations as well as a sample translation for translators of Isaiah 31:8:

• Kupsabiny: “The people of Assyria shall be destroyed through spears,
  and it is not the spears of people.
  A spear that a man did not create
  shall finish those people.
  The people of Assyria shall flee from the spear,
  and their young men shall become slaves.” (Source: Kupsabiny Back Translation)
• Newari: “The Assyrians are about to be felled by a sword,
  which is not the sword from a man.
  With a sword like that they are about to be destroyed,
  [a sword] which does not belong to [lit.: is not of] the men who will have to die.
  They will escape from before that sword.
  And as for their young people, they will be work as slaves. ” (Source: Newari Back Translation)
• Hiligaynon: “Those of/from-Asiria will-die, but not by-means of the sword of a man. They will-flee from war, and their young-men will-become slaves.” (Source: Hiligaynon Back Translation)
• English: “Many of the Assyrian soldiers will be killed,
  but not by swords that men use.
  They will be destroyed by the sword of God;
  and those who are not killed will panic/be very afraid and flee.
  And some of them will be captured and forced to become slaves.” (Source: Translation for Translators)