Over the years, in my fascination with language, I've noticed that nearly every language in the world contains at least one, and sometimes several, words that supposedly defy translation from their language of origin. Quite often, these words are related to the national self-image of the nation from which they derive. I offer below a few examples - feel free to /msg me with suggestions for more.
Portuguese: saudade, "yearning"
Any lusophone you meet will swear by whatever he holds holy that this cannot be translated. It is a special feeling, reserved for speakers of the mellifluous Portuguese tongue.
However, this is not true. The word is easily translated and the concept is fairly universal. Granted, subtle connotations may be missing in the translation, but not, I submit, to any significant degree.
Danish: hygge, "comfiness, cosiness"
It is an article of faith among Danes that no other nation in the world has grasped the concept of spending a pleasant time together quite so well as the Danes themselves. Thus, naturally, the Danes insist that their word for being happy together in a cosey, relaxed fashion is fundamentally untranslatable. I'm a Dane and I'm here to tell you that this is a complete myth.
German: Weltschmerz, "world-weariness", literally "world-pain"
A child of the German Romantic Nationalist movement of the 19th century, the idea that the German soul has a monopoly on feeling agonisingly out of tune with the world. What can I say in response to this myth, except that all teenagers in the world must be German at heart?
Addendum:
I've received quite a lot of feedback on this writeup, including some very good suggestions:
Thanks for the suggestions, all of you.
One issue that deserves to be adressed in this context, however, was raised in achtung_man's well-written and interesting writeup, below, on the Fuegia word mamihlapinatapai. I hesitate to say this, but I really think achtung_man has misunderstood me.
This node is about words that are supposed to be untranslatable. As achtung_man makes quite clear, mamihlapinatapai is translatable - very easily so. The fact that it requires multiple words to translate doesn't mean anything - otherwise, Kuinnginngeeq would deserve to be listed here, too.
The point of listing saudade, hygge and Weltschmerz is that people who speak, respectively, Portuguese, Danish and German will usually claim that you cannot translate them completely. In any other language, you can supposedly only hint at the full meaning of these words.
My opinion, as should be obvious from the above, is that there is no such animal as an untranslatable word.