Great googly moogly
Lynn of Reflections in d minor links to the results of a worldwide survey of 1000 linguists, which asked what words (English or otherwise) are the most untranslatable into other languages. Googly, a tricky pitch (sorry, bowl) in cricket, was number five on the list of untranslatable English words.
A word translates easily when the same concept exists in two different cultures. Sometimes a concept described by a word is unusual but not unheard of in the second, and you might be able to translate the word with a short phrase. When you need a whole paragraph (and possibly photographs and diagrams) to explain a word, you've got something truly untranslatable.
An untranslatable word often becomes a borrowed word, when it corresponds to an idea that has yet to receive a name in the second language. The Arabic word altahmam (a kind of deep sadness) and the Portugese word saudade (a type of longing) might come in handy when trying to express shades of emotion, just as that box of 64 crayons lets you draw with more subtlety than the box of 8.
I tried to find out more about selathirupavar, a Tamil word for a sort of truancy, but a Google search instead turned up versions of the article about untranslatable words in dozens of languages.
I wasn't familiar with one word in the top 10 English untranslatables: bumf, which this site says is short for bum-fodder, a term that goes back to the 17th century to refer to printed matter useful only to be hung in the privy for sanitary purposes. Outdated issues of the Sears Roebuck catalog, for example. Fishwrap comes to mind as a near-synonym. Bumf is ripe for borrowing. I see possibilities in the Latin equivalent anitergium for forming derivative words -- e.g., anitergic literature, which should be filling your mailbox as election day draws near, or which appears on your doorstep daily, if you're a Whirled subscriber.