Is upon the waters: this is not a natural English expression, and the sense of the Hebrew must be “is heard on” or “goes across” the waters. Biblia Dios Habla Hoy has “resounds over the waters,” and New English Bible “echoes over the waters.” Traduction œcuménique de la Bible takes the Hebrew to mean “rules the waters”; the Hebrew can be taken to mean “against the waters.” The waters in line a and many waters in line c may refer to the Mediterranean Sea; some take them to refer to the primeval waters, present at creation (Gen 1.6-7). A general descriptive phrase such as “the seas … all the seas” is to be preferred.
In poetic language the thunder is called “the voice of Yahweh” (see also 18.13). The voice of the LORD, which is used in verses 3 to 9, requires being changed to a verb in some languages where there is no term for voice apart from speaking. Hence it may be necessary to restructure the nominal phrase into a “when” clause; for example, “when the LORD speaks, he is heard on the seas.” In languages in which it is not natural to say that the God of glory thunders, it may be necessary to say “The glorious God speaks like thunder” or “When the glorious God speaks, it is like the thunder of a storm.”
The God of glory: “the majestic, glorious, powerful God” (see “glory” in 26.8). For thunders see the similar passage in 18.13.
Good News Translation has taken The voice of line a as carrying over as the subject of line c (which lacks a verb and which appears to make the LORD the subject); many translations take line c to mean “the LORD is upon the many waters” (see New English Bible, Biblia Dios Habla Hoy); others “the LORD rules the mighty ocean.” It seems better to take The voice (of the LORD) as the subject of line c.
In languages where “speak” instead of “voice” must be used in verse 4, it will often be necessary to say, for example, “When the LORD speaks he shows his power, when he speaks he shows how great he is,” or the second line may sometimes be expressed “when the LORD speaks he shows the people what a great chief he is.”
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 .