Following are a number of back-translations as well as a sample translation for translators of Isaiah 64:3:

• Kupsabiny: “You came down when you did wonders
  and those we did not expect.
  Then the mountains trembled
  on account of you.” (Source: Kupsabiny Back Translation)
• Newari: “At that time you did great work,
  and we did not expect it [lit.: did not have it in mind]
  you came down from there,
  and the mountains trembled before you, shaking with fear.” (Source: Newari Back Translation)
• Hiligaynon: “When you (sing.) came-down in the time-past and did awesome/marvelous things which we (excl.) did- not -expect, the mountains trembled in your (sing.) presence.” (Source: Hiligaynon Back Translation)