Thou art enthroned for ever is literally “you are seated forever,” but this obviously means seated as king, so an easy and effective equivalent is “You reign as king forever” (Good News Translation; similarly Contemporary English Version). In some languages, though, the equivalent will be simply “You reign [or, rule] forever,” since “reign” includes the idea of “king.” In other languages it is necessary to show the object of “reign”; for example, “You rule over everything forever.”

And we are perishing for ever: This clause, which is in contrast to the previous one, is more difficult to understand. For a group of people to be dying for ever can apparently mean one of two things. Is it talking about the death of individuals or the death of the whole Jewish nation? Is the writer grieving that human beings die (as Good News Translation seems to be saying), or that the Jewish nation is in danger of extinction? He could indeed mean just that—that just as God sits eternally enthroned, the Jews, his people, are dying out and once gone, they are gone forever. In this context the second of these interpretations is to be favored. This whole prayer is spoken by the Jewish community about themselves and on their own behalf. Nowhere else in the prayer is the human situation spoken of in the abstract. If we accept this, we could take it to mean “but we are dying out, and will vanish forever.” The reader would take the pronoun “we” to refer to the Jews, as elsewhere in the prayer. This solution will also fit in beautifully with the solution suggested for a larger problem in the next verse (see the comments there). However, if translators disagree with this interpretation, the Good News Translation wording could be expressed more clearly as “but we human beings die and are gone forever.”

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.