The separation of verses 4-6 from the preceding strophe helps identify a structural change. Here the psalmist seems to be addressing his question to Zion, rather than as a reply to the Babylonian captors. This becomes clear in verse 5 with “If I forget you, Jerusalem.” This transition may need to be made more explicit in some languages. One way is to introduce a second heading before verse 4.

In verse 4a “a song of Yahweh” refers to the same song as one of the songs of Zion in verse 3, that is, one of the Temple songs. The phrase a foreign land here has the added implication of “a pagan land”; away from their sacred city (made sacred by the Temple, Yahweh’s earthly dwelling) the Israelites could not sing one of their sacred songs. If, as some believe, the psalmist was already back in Israel when he wrote the psalm (see Cohen, Dahood), verse 4 would be translated “How could we sing…?” Most believe the psalmist was still in exile in Babylonia, but this view overlooks the significance of the change in verb forms. The question in verse 4 is rhetorical and can be translated as a negative statement; for example, “We cannot sing a song to the LORD in a foreign land.”

Quoted with permission from Bratcher, Robert G. and Reyburn, William D. A Handbook on the Book of Psalms. (UBS Helps for Translators). New York: UBS, 1991. For this and other handbooks for translators see here .