The land which I swore to give to their fathers: Good News Translation customarily renders swore as “solemnly promised,” since in English usage the word “swear” can mean “use profanity.” Another way to express the clause here is “the land that I made a strong promise to give to your ancestors.”

They will rule over it essentially means, as Good News Translation puts it, that the land will belong to them again; it will be theirs once more. Israelite territory will again be under Israelite rule.

I will increase them, and they will not be diminished: Increase them means to increase them in numbers, as Good News Translation makes clear with “increase your population” (Contemporary English Version “increase in numbers”). If the third person is used to refer to the people of Israel, this last part of the verse could be rendered “There I will make their population grow, and it will never again decrease.” At this point an introductory “There” may help provide an effective contrast with “There” opening verse 32, if it has been used at that point.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on The Shorter Books of the Deuterocanon. (UBS Helps for Translators). New York: UBS, 2006. For this and other handbooks for translators see here.