Today Translations’ site lists the most untranslatable words, as measured by a poll of a thousand professional translators and interpreters it conducted for the BBC. “Plenipotentiary” won as the most untranslatable English word. The winner among foreign language words is “ilunga [a 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. Note: Tshiluba is a Bantu language spoken in south-eastern Congo, and Zaire].”
However, Lanuage Log is skeptical. “The thing that puzzles me, though, is where Zilinskiene [head of Today Translations] turned up 1,000 linguists who know Tshiluba vocabulary. I’m beginning to get the feeling that this survey might have been a class project in one of Zilinskiene’s Problematics courses…”