Drunkenness increases the anger of a fool to his injury: This means that when a foolish person is drunk and then becomes angry, he is apt to injure himself. Good News Translation expresses it well.

Reducing his strength and adding wounds: Drinking, instead of making the fool stronger, makes him weaker, and causes him to receive more wounds than he would if he were sober.

Contemporary English Version has a helpful model for the verse:

• When fools are drunk,
they become angry and fight,
but their strength is gone,
and so they get hurt.

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.