Following are a number of back-translations as well as a sample translation for translators of Lamentations 4:21:

• Kupsabiny: “People of Edom, you may sneer,
  and you people of Uz may also celebrate,
  but calamity will come to you.
  You will also be stripped to go naked!” (Source: Kupsabiny Back Translation)
• Newari: “O daughter Edom, inhabitant of the land of Uz,
  Rejoice, be happy.
  But that bowl will be given to you also.
  You will be drunk and expose yourself naked.” (Source: Newari Back Translation)
• Hiligaynon: “Alright/Okay, you (plur.) rejoice and be-glad, you people of Edom who live in the land of Uz. But you will-be-caused-to-drink the cup of the punishment of the LORD, and you will-be-drunk and be-naked.” (Source: Hiligaynon Back Translation)
• English: “You people of Edom and Uz,
  you may be happy about what is happening to us now,
  but Yahweh will be punishing you also.
  You will become drunk and will be ashamed
  because your enemies will have stripped off your clothes.” (Source: Translation for Translators)