One of the real struggles in translation is to match diction. Is the original text light, snide, slang-filled, formal, technical, intentionally heightened, obsessively literary? If so, the translator needs to match that tone in the second language, to carry the flavor of the text. But you also don’t want to create something that is so “hip,” so contemporary, that it will feel horribly dated in only a few years. How to balance that? Like every other decision, it is a value judgment, but here’s some thoughtful advice from Rabassa:

Translators, then, are placed in the difficult position of having to be careful not to nail their translation onto the period in which they are living. If the work under way is something contemporary the effect won’t be quite so bad since the original text might well become archaic even sooner than the translation. Like the leaves on trees, words age, yellow, and drop off after a time, although languages, like trees, are divided into different species and the words in one may hold their meaning longer than those in the language into which they are being translated. When I come to translate a “classic” I try to find what we might call “evergreen” words. Translating Machado de Assis […] I try hard to find words that are equally valid in his time and in ours and which, we hope, will endure beyond both ages. A good translation of Cervantes, and there are quite a few, must not be so contemporary that it will eventually become archaic because Cervantes as read today in Spanish is only mildly so. Motteux can sound archaic because he was a contemporary of Cervantes, Putnam cannot. Where Motteux messed up was in not finding as many evergreen words as Cervantes had used. Perhaps he didn’t let Cervantes lead him linguistically. As I discovered translating Machado de Assis and Garcia Marquez, the masters will enable you to render their prose into the best possible translation if you only let yourself be led by their expression, following the only possible way to do. If you ponder you will have lost the path.

From Gregory Rabassa If This Be Treason: Translation and Its Dyscontents, 2005, New Directions Books