The Revised Standard Version literal rendition of the Hebrew makes for a poor English sentence. The meaning is that the Israelites should never do anything, for all time to come, to contribute to the welfare and prosperity of the Ammonites and Moabites. So Good News Translation has “As long as you are a nation, never do anything….”

Their peace or their prosperity: the two nouns mean the same; peace stands here for welfare in general. Traduction œcuménique de la Bible translates “prosperity or welfare,” while New Revised Standard Version has “welfare or prosperity.” The Contemporary English Version rendering “Don’t even think of signing a peace treaty with” is too limited. Good News Translation is better, with “never do anything to help these nations or to make them prosperous.”

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on Deuteronomy. (UBS Helps for Translators). New York: UBS, 2000. For this and other handbooks for translators see here .