Following are a number of back-translations as well as a sample translation for translators of Proverbs 21:31:

• Kupsabiny: “A person may prepare his soldiers,
  but he who makes those soldiers to win (be victorious) is God.” (Source: Kupsabiny Back Translation)
• Newari: “A horse can be made ready for battle,
  but victory or defeat is in the hand of the Lord.” (Source: Newari Back Translation)
• Hiligaynon: “Even the horses are already prepared for war, only the LORD can-cause- to -win.” (Source: Hiligaynon Back Translation)
• Kankanaey: “Even though soldiers prepare their horses for war, it is nonetheless God who is responsible for their winning-the-victory.” (Source: Kankanaey Back Translation)
• English: “We can get horses ready to fight in a battle,
  but Yahweh is the one who enables us to win victories/defeat our enemies.” (Source: Translation for Translators)