Following are a number of back-translations as well as a sample translation for translators of Job 16:21:

• Kupsabiny: “He is pleading for me to God
  like a man speaks for his friend.” (Source: Kupsabiny Back Translation)
• Newari: “As a person makes an entreaty for his friend,
  [he] makes an entreaty to God for a mortal man,” (Source: Newari Back Translation)
• Hiligaynon: “My witness is-the-one-who will-plead-for-mercy to God for me like a man who pleads-for-mercy for his friend.” (Source: Hiligaynon Back Translation)
• English: “I pray that the one who knows what I have done would come to plead with God for me
  like people plead for their friends.” (Source: Translation for Translators)