Idioms and Metaphors
I think I finally understand how you can tell the difference between metaphors and idioms.
Idioms can't be translated over from one language to another because they lose there meaning so saying "They are going out and painting the town red" can't be translated because saying "They are going out and coloring the town ruby" does not make sense.
Metaphors can be translated from one language to another and subsituting synonyms it still does not loose all it's literal meaning. You can say "She put her money where her mouth is" and subsititute cash for money and people will still get what is trying to be said "She put her cash where her mouth is".