Every firstling of an ass means “every first-born male donkey” (Good News Translation). “Male” is implied from verse 12. (“Donkey” was described at 4.20.) You shall redeem uses a word meaning to “buy back” (Good News Translation) by paying a ransom. In languages where there are specific terms describing the “buying back” or “ransoming” of a slave, they will probably be appropriate here. The law for buying back firstborn animals reflects Yahweh’s deliverance of (or, setting free) the Israelites from slavery. In the context of this verse, a lamb is used for buying back the donkey. (A different word with the same meaning is used in 6.6.) You is singular. Here the ransom is a lamb, which really means “a lamb or a kid,” as New Jerusalem Bible, New English Bible, Revised English Bible, and Translator’s Old Testament make clear (so also at 12.3). By implication this is done “by offering a lamb in its place” (Good News Translation). Contemporary English Version makes this more explicit with “sacrificing a lamb.” This may also be expressed as “by slaughtering a lamb and offering it….”

Or if you will not redeem it refers to the ass and gives an alternative, so Good News Translation has “If you do not want to buy back the donkey.” You shall break its neck means the neck of the donkey. Every first-born of man distinguishes human beings from the animals. (The Hebrew ʾadam [man] is generic, meaning humankind.) Your sons simply refers to every “male child of yours” (Good News Translation). You shall redeem uses the same word again, but the text does not say how this is to be done. However, in some languages it will be necessary to make it explicit that the son is bought back from the LORD; for example, “buy back every firstborn son from the LORD.”

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .