He made him hear his voice: New Revised Standard Version is better with “He allowed him to hear his voice” (similarly Good News Translation). But in some languages it will be helpful to repeat Moses’ name again; for example, “He allowed Moses to hear his voice [or, hear him speak].”

And led him into the thick darkness may be rendered “led him into the thick dark cloud.” The reference is to Exo 20.21. The use of the in English signifies that this is a cloud that is known to the author and his readers. In some languages this line will be translated “and led him into that thick dark cloud.” Each language will have a way to indicate that this is information known to the author and his readers.

And gave him the commandments face to face may be rendered “There he saw the Lord face-to-face and received the commandments” or “where, face-to-face, the Lord gave him the commandments.” Compare Exo 33.11.

The law of life and knowledge: The relation between the law and life and knowledge is clarified in Good News Translation, which has “the Law that gives life and knowledge.” New English Bible is similar with “a law that brings life and knowledge.”

To teach Jacob the covenant, and Israel his judgments: Here both Jacob and Israel refer to the nation of Israel, as Good News Translation makes clear with “the Israelites.” While Good News Translation has “so that Moses might teach…,” the Greek has the Lord giving the law so that he, the Lord, might teach Israel. We could say “so that the Israelites might learn….” For covenant see 17.12. Judgments here refers to the laws within the covenant, which is why Good News Translation says “covenant regulations.” For this line we could say “so that he [the Lord] might teach the Israelites the terms of his covenant [or, agreement] with them.”

Alternative models for this verse are:

• He allowed Moses to hear his voice and led him into the thick black cloud. There he saw the Lord face-to-face, and the Lord gave him the commandments, the Law that brings life and knowledge. He did this so that the Israelites might learn these covenant regulations [or, commands].

• … The Lord did this so that he [the Lord] might teach the Israelites the terms of his covenant [or, agreement] with them.

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.