In line a Good News Translation takes rejoice in God to mean “rejoice because of what God has done”; in this context it refers to the king’s victory over his enemies.
All who swear by him is misleading in English, since “swear” in normal usage means profanity. The meaning is to “make promises” or “take an oath” in God’s name. Bible en français courant translates “take an oath, calling on God as witness.” By him can refer either to God (Briggs, Kirkpatrick, Weiser, Dahood, New English Bible, New Jerusalem Bible) or to the king (Anderson, Toombs). Many translations (see New Jerusalem Bible, Traduction œcuménique de la Bible, New American Bible, An American Translation, Revised Standard Version, Biblia Dios Habla Hoy) leave the phrase ambiguous, which is not to be recommended. One could “swear by the king” (see 1 Sam 17.55; 25.26; 2 Sam 11.11; 15.21), but it seems more likely that here God is meant.
The term swear in all who swear by him refers to the taking of an oath when making a statement or promise, and is expressed variously in different languages. Such terms are often related to speaking, touching (such as touching an object when taking an oath), and cursing oneself or calling on God or the object touched to curse the speaker if the promise is not kept or the statement is not true. Swear by him or “make promises in God’s name” must often be recast in translation to say, for example, “everyone who makes a promise and speaks God’s name to remove any doubts will praise God” or “all who say ‘I will do this,’ and confirm it by saying it in God’s name, will rejoice.”
Shall glory: meaning “will praise God”; or an intransitive verb can be used in translation, “will rejoice, will exult.”
Good News Translation makes clear the contrast between those who swear or make promises in God’s name in the second line, and the liars in last line. Translators should make the contrast clear.
The mouths of liars will be stopped: this could be a way of speaking about their death (Cohen, Dahood), or else that their lies will be exposed and they will have to keep quiet. It seems more likely that the latter is meant. Mouths of liars will be stopped is a passive construction which must be recast in some languages as active. In such cases it is possible to say, for example, “God will close the mouths of liars.”
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 .