Idiomatic--what a great word. And yet, it doesn't mean "machine that clanks out idiots automatically," which would be cool in a Dr. Seuss/Willy Wonka kind of way.
No matter, though. Idioms are still great fun. Even though the book I'm Not Hanging Noodles on Your Ears isn't a grammar reference, people who love language are going to get a kick out of it. Written by Jag Bhalla and published by National Geographic, it's amusing, surprisingly deep, and explains the importance of idioms nicely: "Languages make visible what's important to their users." In it you'll find a collection of 1,000 or so idioms from languages around the world, along with brief, insightful essays to put things in context.
Some of the idioms are funny. The French call a man who is attracted to any woman the "lover of a goat whose hair is combed."
Some will give you a little pang. "To eat like a child of God" (i.e., an orphan) is to eat quickly in Mexico of Spain. Meanwhile, children are "fruit of heaven" in Hindi. But an unexpected, not altogether welcome event is "a daughter of yesterday" in Arabic. Ouch.
It's an especially useful book for fiction writers looking to give life to their characters. Do check it out.