Following are a number of back-translations as well as a sample translation for translators of Isaiah 44:23:

• Kupsabiny: “Let up there in the sky sing because of what God is doing.
  Let also what is here on earth sing.
  Let the mountains sing with joy.
  Let the forest and every tree of the forest sing.
  Because God redeems the stomach of Israel
  and shows his greatness in Israel.” (Source: Kupsabiny Back Translation)
• Newari: “O heavens, sing a song of joy. The LORD has done this.
  Sing loudly, O depths of the earth!
  O mountains, forests and all the trees that are there,
  sing loudly,
  for, having paid the price, the LORD has set Jacob free.
  He shows his glory through his act of saving Israel.” (Source: Newari Back Translation)
• Hiligaynon: “You (sing.) sing for joy, O heavens! Shout aloud, O earth! You (plur.) sing mountains, and trees in the forest. For the LORD will- surely -do this. He will-save the descendants of Jacob; he will-show his greatness in Israel.” (Source: Hiligaynon Back Translation)