Following are a number of back-translations as well as a sample translation for translators of Isaiah 55:12:

• Kupsabiny: “You (plur.) shall go out in happiness,
  and you will be led forth in peace.
  The mountains and hills shall sing
  in front of you (plur.).
  All the trees shall clap
  their hands with joy.” (Source: Kupsabiny Back Translation)
• Newari: “You will have the chance to live in joy and peace.
  Even the mountains and hills will start to sing for you,
  and on the plains [lit.: staying in the level-going place] the trees will begin to clap their hands.” (Source: Newari Back Translation)
• Hiligaynon: “‘Israelinhon, you (plur.) will-leave from Babilonia with joy, and I will-lead you (plur.) that you (plur.) will- not -be-harmed. As-if the mountains will-sing for joy, and as-if all the trees will-clap(-their-hands).” (Source: Hiligaynon Back Translation)