Behold, I will shake my hand over them: Behold may be expressed as “Look!” or “Pay attention!” in some languages, but in other languages it will be better to omit it or say, “I myself will shake….” Shaking the hand over someone is a gesture that threatens hostile action (compare Isa 11.15; Isa 19.16). Good News Translation drops the form of the gesture and translates its meaning as “fight against.” New Living Translation retains the gesture and also explains its meaning with “I will raise my fist to crush them.” Them refers to “the nations who plundered you” in the previous verse.
When the LORD fights against them, their power will be ended, and they shall become plunder for those who served them. Those who had been oppressed will be avenged. Those who served them refers to captive nations, especially the Jews. Another way of saying this is “The people who once served them [or, were their slaves] will take their possessions by force.”
Then you will know that the LORD of hosts has sent me: Zechariah is saying that when the events he foretold came true, then his authority as a prophet would be proved genuine. This statement is repeated in verse 11; 4.9; 6.15. These words are somewhat awkward here in the middle of the paragraph because they refer to the prophet as me in a setting where the LORD has been speaking of himself in the first person. Stylistic oddity is not uncommon in Zechariah. The similar expression in verse 11 is certainly part of the message, so it seems best to treat these words also as part of the message despite the clumsiness at the discourse level. This is the interpretation of Revised Standard Version/New Revised Standard Version, Jerusalem Bible, New English Bible/ Revised English Bible, Beck, New Living Translation, and Contemporary English Version.
From this perspective, the punctuation of Good News Translation is misleading in this verse. Good News Translation considers that the words of the LORD stop at those who served them, and that the quotation marks should be closed there, as do Moffatt, New Jewish Publication Society’s Tanakh, Bible de Jérusalem, Bible en français courant, Die Bibel im heutigen Deutsch, and Parola Del Signore: La Bibbia in Lingua Corrente. The remaining part of the verse, Then you will know that the LORD of hosts has sent me, is taken by Good News Translation as a comment by the prophet rather than as part of his message. If this interpretation is followed, then it may reasonably be set out as a separate statement, as in Good News Translation and Bible en français courant. But this option is not recommended.
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 .