If a metaphor is potentially understandable in the target language, why should be change it, even if its never been used in English elsewhere?

Dying metaphors. A newly invented metaphor assists thought by evoking a visual image, while on the other hand a metaphor which is technically “dead” (e.g. iron resolution) has in effect reverted to being an ordinary word and can generally be used without loss of vividness. But in between these two classes there is a huge dump of worn-out metaphors which have lost all evocative power and are merely used because they save people the trouble of inventing phrases for themselves. Examples are: Ring the changes on, take up the cudgel for, toe the line, ride roughshod over, stand shoulder to shoulder with, play into the hands of, no axe to grind, grist to the mill, fishing in troubled waters, on the order of the day, Achilles’ heel, swan song, hotbed. Many of these are used without knowledge of their meaning (what is a “rift,” for instance?), and incompatible metaphors are frequently mixed, a sure sign that the writer is not interested in what he is saying. Some metaphors now current have been twisted out of their original meaning without those who use them even being aware of the fact. For example, toe the line is sometimes written as tow the line. Another example is the hammer and the anvil, now always used with the implication that the anvil gets the worst of it. In real life it is always the anvil that breaks the hammer, never the other way about: a writer who stopped to think what he was saying would avoid perverting the original phrase.

George Orwell “Politics and the English Language“

I say, if the metaphor, no matter how foreign it is, successfully assists thought by evoking that visual image, keep it in the text. If it hinders thought rather than assisting, replace it with one that does – but maintain the poetic* style of the source text. That means, try to avoid dying metaphors and don’t use ones that have lost their power.

*I use the term “poetic” rather loosely to refer to any kind of creative language.