As inscrutable as a corporate idiom
Cut corners, up to speed, circle back, crunch the numbers, ballpark figure—we use idioms a lot in English, particularly at work. Ad idiom is defined as a phrase that has "a meaning that cannot be derived from the conjoined meanings of its elements”.
I believe idioms are baked into corporate culture because they're indirect, and therefore perceived as more polite. But they can get you into hot water (hey, that's an idiom) if you use them too frequently or in the wrong situation.
As confusing as a Pope
Idioms aren't endemic to English, many languages lean on them heavily to communicate (further proof that the purpose of language isn't to get from A to B by the quickest route possible).
As idioms function in the abstract, the speaker needs a great deal of constructed cultural knowledge to make sense of them and without it, idioms can be inscrutable to an outsider.
For example, the Italian version of 'once in a blue moon' is 'ogni morte di papa', literally 'every death of a Pope'. But then, how often does a Pope die? Popes are quite old when they take office but perhaps the advent of modern medicine has increased the length of the average papacy? Do the long robes present a tripping hazard? It’s a tricky one to judge without Wikipedia open to the official list of Popes and when they died.
As bamboozling as a loaded plate
A misunderstanding over Popes while trotting out your high school Italian is one thing. But when idioms creep into emails, memos, and offices, they can really interfere with the business of business. Rather typically, the German idiom for 'everything must end' is 'Alles hat ein ende, nur die wurst hat zwei' which literally means 'everything has one end, only the sausage has two'.
Imagine you're living in Germany, trying to learn the language, trying to run out the clock (idiom) at work, and someone in a meeting tells you a sausage has two ends. What they're trying to say is you're fired, what you hear is a German going on about a double-ended sausage.
Here's another example. In English, having a lot on your plate at work is not a good thing, it means you're busy and at capacity. But in other cultures, could having a lot on your plate be seen as a positive thing? I think so. Couldn’t a loaded plate be a reference to abundance, like a cup that’s runnething over? There's definitely room for misinterpretation.
The lesson here is idiom awareness. It's impossible to avoid idioms, they're the keyboard shortcuts of language and can be quite fun. But when writing to an international audience, to someone you don't know, or when you just want to be reallllllly clear, don't use idioms. Say what you mean.
TL;DR? Idioms can be confusing; use them kindly.