I will not drive them out is literally “I will not drive him out,” but English demands the plural them. From before you is almost identical with verse 28 and need not be repeated. In one year means “in a single year” (New Jewish Publication Society’s Tanakh, New International Version, New Jerusalem Bible), “within one year’s time” (Good News Translation), or “in the first year” (Contemporary English Version). Lest the land become desolate means “or the land would become desolate” (New Revised Standard Version). Good News Translation renders it as “If I did, the land would become deserted.” One may also say “in order that the land will not become a wasteland.”

And the wild beasts multiply against you is literally “and the animal of the field will become numerous over you [singular].” The same expression for wild beasts is used in verse 11. One may also say “animal of the field” or “jungle [or, forest] animals.” This clause is still influenced by the word lest, so one may say “and in order that the wild animals will not become too many for you.” New American Bible relates the two clauses as cause and effect: “else the land will become so desolate that the wild beasts will multiply against you.” Multiply against you is usually understood as “be too many for you” or “wild animals would be everywhere.”

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .