Following are a number of back-translations as well as a sample translation for translators of 1 Samuel 20:42:

• Kupsabiny: “Jonathan told David that, ‘Brother, go in peace. God knows the agreement we made together and it will go/continue like that forever.’
  Then David left. After that, Jonathan went back home.” (Source: Kupsabiny Back Translation)
• Newari: “Then Jonathan said to David, "Go with happiness, the LORD, in whose name we have sealed a covenant will be a witness between you and me, between your descendants and my descendants forever." Then David immediately went from there. Jonathan, however, returned to the city.” (Source: Newari Back Translation)
• Hiligaynon: “Then Jonatan said to David, ‘Okay, go in peace/[lit. go just well]. And may the LORD help us (incl.) that what we (incl.) have-sworn to him as friends will- not -be-undone forever (between) our (incl.) descendants.’ Then David went-(out), and Jonatan on-the-other-hand returned to the town/city.” (Source: Hiligaynon Back Translation)
• English: “Jonathan said to David, ‘May things go well for you as you go. Yahweh has heard what we solemnly promised to always do for each other, and what we said that our descendants must do for each other.’ Then David left, and Jonathan went back to the town.” (Source: Translation for Translators)