Good News Translation reverses the lines in this verse.

He that takes vengeance will suffer vengeance from the Lord means that the Lord will punish the people who take vengeance on (or, pay back) others. Good News Translation says “if you take vengeance on someone, the Lord will take vengeance on you.” We may also translate “if you take revenge on someone, the Lord will punish you.”

And he will firmly establish his sins: As the Revised Standard Version footnote indicates, some Greek manuscripts read “he will closely observe his sins,” that is, the Lord will closely observe the sins of the person who takes vengeance. This reading is much to be preferred. It is found in Good News Translation and most newer translations. We think a textual footnote is unnecessary.

An alternative model for this verse is:

• The Lord takes careful note of [or, closely observes] your sins, and if you take vengeance on someone, he will punish you.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Sirach. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here.