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Comment by auganov
I'll have to agree with this comment by "Jason":
You may as well claim "go kill yourself" is an idiom that means "I don't like you". An idiom is when it's nearly impossible to infer the actual meaning based off the literal meaning of the words. A hyperbole or a metaphor does not make an idiom. Death is invoked here exactly because of what it implies. "Death to X country" is not any less metaphorical in English. A country obviously cannot die.