Following are a number of back-translations as well as a sample translation for translators of Joel 3:12:

• Kupsabiny: “God is saying,
  ‘Let the communities prepare themselves
  and come to the valley of Jehoshaphat.
  I will sit there
  and judge all the neighboring communities.” (Source: Kupsabiny Back Translation)
• Newari: “‘Let people be aroused
  to come to the valley of Jehoshaphat.
  Because there I will sit to
  judge all the surrounding nations.” (Source: Newari Back Translation)
• Hiligaynon: “The LORD said, ‘The nations in the surrounding must be-challenged to go to the Valley/Plains of Jehoshaphat, for I will-judge them there.” (Source: Hiligaynon Back Translation)
• Kankanaey: “Then God continued to say, ‘The nations must get-ready so-that they will go to the Valley/Plain of Judging. Because there, I will judge in-the-future all nations.” (Source: Kankanaey Back Translation)
• English: “The people in the nations near Judah must get ready and come to the Valley of Judgment.
  There Yahweh will sit and judge and punish them.” (Source: Translation for Translators)