The Hebrew of this verse speaks of “Ai and Bethel” (see Revised Standard Version; Good News Translation footnote); the Septuagint omits “and Bethel,” which Good News Translation, New English Bible, Jerusalem Bible follow; there seems to be no reason for supposing that the men of Bethel were involved in this campaign. Hebrew Old Testament Text Project favors the Hebrew text, and a translator should feel free to follow it. Ai was left unprotected, an easy target for the Israelite troops lying in ambush west of the city.

Went after represents two verbs in Hebrew (Revised Standard Version “go out after … pursued”). Some languages will require the retention of two verbs, one indicating departure from the city and the other the actual pursuit of the Israelites.

The city was left wide open refers specifically to the city gates. One may then translate the verse “Every man in Ai left the city and ran after the Israelites. There was no one left to defend the city, and the gates of the city were left wide open.” Or “… and the men of the city had left the gates wide open.”

Quoted with permission from Bratcher, Robert G. and Newman, Barclay M. A Handbook on Joshua. (UBS Helps for Translators). New York: UBS, 1983. For this and other handbooks for translators see here .