Understanding their “second language’s” culture is a must for translators. A professor from University used to tell us: “Navidad is an easy word to translate: we look it up in the dictionary and there it is: Christmas. But phrases like “Christmas mood” (humor o atmósfera de Navidad) or “Christmas landscape” (paisaje navideño) are not going to express the same sentiment in Spanish (or Finnish, or Russian…) as they do in English, given that the whole “Christmas experience” is not the same in every country. While Christmas is celebrated in the middle of summer in the southern hemisphere, the U.S. and other European countries with their falling snow and various traditions have a very different experience.
Having a dictionary is not enough for translating well. It is not only about translating words. For example, you could learn the words poner and pilas, but still not understand the meaning of the idiom ponerse las pilas. One also has to know about the particular phrases that require one special combination of terms (collocations) and not another: though people would most likely understand Prospera Navidad, this combination, while not technically “wrong,” would sound as strange as Happy Christmas or Merry Birthday.
One must take cultural references into account. A friend once had the task of translating a book for veterinarians in which there were instructions for a certain procedure for rabbits that had to be done “in January and February.” But if this was translated for the southern hemisphere, then January and February (summer in the southern hemisphere) would be the wrong time of year, with who knows what consequences for the poor animals. (In this situation, she decided to add “in the northern hemisphere” in parentheses and let the veterinarians figure out that it should be done in July-August if they are in the southern hemisphere.)