They refers to the people of Israel, not the enemy of verse 11.

Sing aloud: See verse 7.

The height of Zion is “Mount Zion” (Good News Translation).

They shall be radiant over the goodness of the LORD: Be radiant translates a verb meaning “shine,” and is used elsewhere only in Psa 34.5; Isa 60.5. Good News Translation renders it “delighted,” which is certainly acceptable, but if the image of faces shining with happiness is meaningful in a language, then translators should keep it, and say something like “Their faces were shining because of all the good things they were going to receive from the LORD.”

Good News Translation interprets the goodness of the LORD as the “gifts” that follow: the grain, the wine, and the oil … the young of the flock and the herd. New Jerusalem Bible and New American Bible also make this meaning clear. It is important, as in Good News Translation, to make it clear that oil is “olive oil,” to distinguish it from other types of oil, particularly from petroleum. If olives are unknown, translators can use an expression such as “rich [or, fine] cooking oil.” As Good News Translation makes clear, the flock refers to “sheep,” and the herd refers to “cattle.”

Life translates the word most often rendered “soul” in the Old Testament. The construction their life is legitimately rendered “They” (Good News Translation, Revised English Bible) or “They themselves” (Bright, New American Bible).

A watered garden: This is better rendered as “a well-watered garden” (Good News Translation, Bright). The phrase is found also in Isa 58.11.

They shall languish no more: The verb languish occurs again in verse 25, but elsewhere in the Old Testament only in Psa 88.9, where Revised Standard Version renders it “grows dim” (of a person’s eye). Here New Jerusalem Bible and New International Version have “they will sorrow no more.” Another good rendering is “they will have no reason to be dispirited [or, discouraged].” Good News Translation has carried this forward logically with “they will have everything they need.”

Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on Jeremiah. (UBS Helps for Translators). New York: UBS, 2003. For this and other handbooks for translators see here .