Thanks a lot to Zoe for bringing my attention to this article on the most untranslatable words in the world (full article here).
The winner is….
ilunga : Tshiluba word for a person who is ready to forgive any abuse for the first time; to tolerate it a second time; but never a third time.
However, I find it odd that the “most untranslatable” English word was voted to be plenipotentiary… I suppose the concept of a person representing a country or organisation, however familiar it is in Western societies, might not be shared worldwide.