Just as she rejoiced at your fall and was glad for your ruin: The pronoun she refers back to “the city” in verse 32. Good News Translation named Babylon as the city in verse 32, and here refers back to it as “that city.” Contemporary English Version repeats “Babylon” from the previous verse. New English Bible has “The same city.”

So she will be grieved at her own desolation: Her own desolation is a prediction of the fall and depopulation of Babylon. It points forward to the first line of the next verse. In some languages her own desolation may be rendered “she is now empty of people,” or translators may express the whole line as “now she will be mourning when she herself lies empty with no people in her.”

In rendering this verse, both Good News Translation and New English Bible have insight (see above), which can be combined effectively as follows:

• That same city that rejoiced when you fell, that took such delight in your ruin, will be mourning when she herself is deserted [or, stands empty].

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.