Revised Standard Version keeps verses 21-22 in the one long sentence that begins in verse 18. It is better to break up the material into several sentences.

As a result of the LORD’s activity, there will be rejoicing in Jerusalem, where peoples and kingdoms will gather to worship (literally “serve”) Yahweh. In verse 21a to declare … the name of the LORD means to acclaim him, to proclaim the great things he has done; and in verse 21b declare … his praise may be simply “praise him,” or else “declare why he must be praised.” It should be clear in verse 22 that this universal gathering of peoples and kingdoms will take place in Jerusalem. In many languages it will be preferable for the translator to avoid the exclusivist language of men may declare and say “people will….” In verse 22 it will often be necessary to express the subject as “people from many nations and kingdoms.”

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 .