Both of these phrases mean basically the same thing. Isaiah compares the enemy army to a lion to imply how the sound of their attack will cause the people of Judah to be very afraid. AT: "When their army shouts in battle they will sound like a roaring lion" (See: [[rc://en/ta/man/translate/figs-parallelism]] and [[rc://en/ta/man/translate/figs-simile]])
A young age is a metonym for strength. AT: "the strongest lions" (See: [[rc://en/ta/man/translate/figs-metonymy]])
# They will growl and seize the prey
Isaiah compares the enemy killing the people of Judah to a lion killing a weaker animal. Possible meanings are 1) lions make a sound not as loud as a roar just before they strike, or 2) the writer is using two words to mean the same thing. (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-doublet]])
These are the same word translated "growl" in verse 29. Use your language's word for the sound of waves in a storm or heavy rain or some other frightening natural sound.