Following are a number of back-translations as well as a sample translation for translators of Deuteronomy 27:20:

• Kupsabiny: “‘Cursed is any man who sleeps with the wife of his father and shames his father.’ Then all the people are to respond, ‘It is/shall be like that!’ (Amen).” (Source: Kupsabiny Back Translation)
• Newari: “A curse must fall on the man who sleeps with his father’s wife, for he has shamed his father.
  Then all must say, "Amen!"” (Source: Newari Back Translation)
• Hiligaynon: “‘Cursed is the man who has-sexual-relation with the wife of his father, for he dishonors his father.’ Then all the people shall-reply, ‘Amen!’” (Source: Hiligaynon Back Translation)
• English: “‘Yahweh will curse anyone who shows no respect for/disgraces his father
  by having sex with any of his father’s wives.’
  And all the people must reply, ‘Amen/We want that to happen.’” (Source: Translation for Translators)