I've already touched on untranslatable words in a previous post, but the truth is that "translatability" as a general concept doesn't really exist at all. At best, translation is merely a form of approximation. It's all about finding the "closest match" to a word in a different language, and when you do that, chances are that some subtle aspect of the original word-- perhaps its connotation, or maybe an extra layer of meaning, or something encoded in the actual sound of the word-- will be lost. This is perhaps best seen in words that describe family relations, like the Icelandic word feðgar.