The phrase "lift up their voices" is an idiom that means to speak loudly. AT: "They will sing and shout about the majesty of Yahweh" (See: [[rc://en/ta/man/translate/figs-idiom]])
Here "the sea" refers to the Mediterranean Sea which is west of Israel. AT: "and those in the west towards the sea will shout with joy" (See: [[rc://en/ta/man/translate/figs-explicit]])
The phrase "in the east" represents the people living east of Israel. Isaiah is commanding these people as if they were there with him. But, he is talking to the people in the future after God devastates the earth. AT: "Therefore everyone from distant lands in the east will glorify Yahweh" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-apostrophe]] and [[rc://en/ta/man/translate/figs-pastforfuture]])
Isaiah is commanding the people who live on the islands in the Mediterranean sea as if they were there with him. But, he is talking to the people in the future after God devastates the earth. AT: "everyone in the islands will give glory" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-apostrophe]] and [[rc://en/ta/man/translate/figs-pastforfuture]])