On that day, says the LORD: The words On that day mark the beginning of the next subparagraph. Says the LORD represents the formula neʾum YHWH. Here, as in 13.2, it has the function of reinforcing On that day as a marker for the beginning of a new unit. The Hebrew word translated says is actually a noun, and some versions render this formula as “oracle of the LORD” (Bible de Jérusalem, Traduction œcuménique de la Bible). This may be a possible approach in other languages. Since this phrase does carry some information at the discourse level, it is preferable not to omit it entirely as Good News Translation, Contemporary English Version, and Die Bibel im heutigen Deutsch do. So we recommend that translators keep both phrases. In some languages the order may be reversed; for example, “The LORD says, ‘On that day….’ ”

I will strike every horse with panic, and its rider with madness: The LORD will intervene in the siege of Jerusalem on behalf of his people by causing chaos in the army of the attackers, especially the cavalry. Panic means excessive, unreasoning, and overwhelming fear (compare 14.13). In this case the unreasoning fear probably causes the horses to turn around and flee from the battlefield. Other ways to translate panic are “they will be terrified,” “they will have hearts full of fear,” and “their hearts/livers will fall [or, be cold] with fear.” The words for panic and madness (and indeed blindness later in the verse) are rare terms that all occur together in Deut 28.28 (where Revised Standard Version has “confusion” instead of panic). The context there is the curses that the LORD promised to bring on his own people if they disobeyed the Law. By referring so clearly to that passage, Zechariah is saying that the curses originally threatened against Israel will be turned upon their enemies. Compare 2 Kgs 6.18. For “go crazy” in the American editions of Good News Translation, the British and Australian editions have “go mad.” No difference in meaning is intended.

But upon the house of Judah I will open my eyes: The house of Judah is a figure of speech called a metonymy, and means “the people of Judah.” When the LORD acts against the army of those besieging Jerusalem, he will spare the people of Judah who are (probably against their will) part of that army. To open my eyes upon someone means to show favor to them (compare Solomon’s prayer in 1 Kgs 8.29). Good News Translation puts this into modern language as “I will watch over the people of Judah” (similarly Contemporary English Version). New Revised Standard Version tries both to convey the meaning and to keep the picture with “But on the house of Judah I will keep a watchful eye” (similarly New International Version). Some languages may have a similar idiom.

When I strike every horse of the peoples with blindness: The blindness of the horses may be the reason for their panic mentioned earlier. In more modern English we might say “I will make every horse in the enemy army blind.” There is no textual justification for the omission of the word “horse” from Bible de Jérusalem and New Jerusalem Bible so as to say that the LORD makes the people blind. Contemporary English Version, without a footnote, omits this final sentence. This may be a misprint, but in any case translators should not leave it out.

Quoted with permission from Clark, David J. & Hatton, Howard A. A Handbook on Zechariah. (UBS Helps for Translators). New York: UBS, 2002. For this and other handbooks for translators see here .