Newman offers this obiter dictum regarding translation in his 15th Oxford University Sermon:
Language is a sort of analysis of thought, and, since ideas are infinite, and infinitely combined, and infinitely modified, whereas language is a method definite and limited, and confined to an arbitrary selection of a certain number of these innumerable materials, it were idle to expect that the courses of thought marked out in one language should, except in their great outlines and main centres, correspond to those of another. Multidues of ideas expressed in the one do not even enter into the other, and can only be conveyed by some economy or accommodation, by circumlocutions, phrases, limiting words, figures, or some bold and happy expedient (Genius of Newman, 208-9).
Newman is a modest pessimist about the prospects for translation, but his modesty saves him from disaster: what one language expresses succinctly and vividly, another expresses only with difficulty (for instance, Sehnsucht, the German word whose connotations C.S. Lewis needed a string of English sentences to capture to his satisfaction). But it’s in principle true that any idea (or proposition) expressible in one language is expressible in any other (the translatability criterion of languagehood, we might call it). It’s perfectly possible for a language not to have a express term for something its speakers have never encountered (many equatorial languages have no word for “snow,” for obvious reasons), but that language will have the internal resources to devise a way of picking out the thing in question; and of course languages are constantly shedding and growing new words, in part to meet such changing circumstances.
In Le Ton Beau de Marot (hear the pun?), a book on translation, Douglas Hoftstadter offers a nice image to capture this modest pessimism. Translating an essay or even a paragraph from one language to another is a bit like attempting to reproduce a mosaic composed of square tiles using hexagonal tiles — of course it’s possible to achieve a general, good-enough correspondence between the two images, but the adequacy of that resemblance decreases with the sized of the area compared. Meaning: word-for-word translation, especially one that seeks to reproduce formal features of language such as rhyme or puns, or connotation rather than denotation, is mostly hopeless; but that’s no obstacle to idea-for-idea translation.