Following are a number of back-translations as well as a sample translation for translators of Isaiah 45:21:

• Kupsabiny: “Arrange/prepare your words to be heard
  and ask one another.
  Who has said beforehand long ago what would happen?
  Is it not me, God?
  There is no God except me,
  a God who is righteous and who saves you.” (Source: Kupsabiny Back Translation)
• Newari: “Now talk about what is about to happen,
  Take counsel among yourselves.
  Who told you [of] this matter many years ago?
  Who has told you in the distant past?
  What! Was it not I, the LORD?
  Besides me, there are no other God.
  A righteous and savior God,
  besides me, there is no other.” (Source: Newari Back Translation)
• Hiligaynon: “You (plur.) consult-each-other, and reveal/present your (plur.) case. Who foretold/predicted before the things that will-happen? Is it not I, the LORD? There is no other God but I alone — the righteous God and Savior.” (Source: Hiligaynon Back Translation)