The LORD was so angry with Aaron: for God’s anger against Aaron see Exo 32.1-16, 21-25, 35. But nothing is said there of Moses’ intervention on Aaron’s behalf. Good News Translation is a good model.

It is possible to combine verses 18-20 as follows:

• I lay prostrate on the ground before the LORD [or, at the place of worship] and prayed to him for you [plural] as I did before. I didn’t eat or drink for forty days and nights. You had committed a terrible sin by making that idol, and I was afraid that the LORD was angry enough with you and Aaron to destroy you. So I prayed for you and Aaron as I did before, and the LORD again answered my prayers.

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on Deuteronomy. (UBS Helps for Translators). New York: UBS, 2000. For this and other handbooks for translators see here .