Following are a number of back-translations as well as a sample translation for translators of Isaiah 51:11:

• Kupsabiny: “So, the people God will save shall return
  coming to Zion while singing.
  They shall always rejoice,
  be happy and ululate.
  Trouble and screams shall be over where they are.” (Source: Kupsabiny Back Translation)
• Newari: “Those whom the LORD has set free by paying the price will be about to come back again.
  They will come into Zion singing songs,
  and everlasting joy will be the crown of their heads.
  They will get to take joy and rejoicing. Then mourning and groaning will be far from them.” (Source: Newari Back Translation)
• Hiligaynon: “The ones- whom- you (sing.) -have-redeemed will-return to Jerusalem with singing, that their happiness/joy never stop. Their sadness will- now -vanish/disappear, and their joy will-overflow.” (Source: Hiligaynon Back Translation)