A paragraph break is needed here (so Good News Translation); the subject changes to the woman who commits adultery.

So it is with a woman who leaves her husband and provides an heir by a stranger: The woman here does not actually leave her husband. Since she presents her husband with another man’s child, she obviously is still living with her husband. She has an affair with another man without her husband’s knowledge. In English we would say she “is unfaithful to her husband” (Good News Translation; compare verse 18). It would have been easy for ben Sira to say “child,” but he deliberately says heir. It is not just that the husband has been duped; when he dies, part of his belongings will go to a child that is not even his. This means his own sons will be cheated out of part of their rightful inheritance. Making this point clear in translation may involve being wordy, but it is worth it. Stranger is not what is meant. The adulterer may be well known to the husband, no stranger at all. The point is that the child the woman has is not her husband’s child. A possible approach to this whole verse is:

• The same is true of a woman who is unfaithful to her husband and gives birth to another man’s child—a child who will some day inherit his [the husband’s] property.

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.