When Bacchides learned of this: The demonstrative pronoun this refers to the Jewish people choosing Jonathan as their leader. So we may express this clause as “When Bacchides heard that the people had chosen Jonathan as their new leader.”

He tried to kill him does not imply that there was an occasion when Bacchides tried to kill Jonathan but was not successful. It means that he began an effort to kill him. New English Bible has “he set himself to kill Jonathan.” New Jerusalem Bible translates “Bacchides … made plans to kill Jonathan.” Good News Bible uses “he made up his mind to kill Jonathan.” Contemporary English Version says “Bacchides plotted to kill Jonathan.” Any of these approaches will work.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.