Both. Some will say a “Science” and others an “Art.” Most of the time, those who actually translate will say it is a science in some ways, but definitely an art form in the end. The “science” aspect involves following certain rules like grammar and sentence structure in your target language, and using technology as an indispensable tool in today’s world. Tools like Machine Translation (think Google Translate), and CAT Tools (software that keeps track of translations to be used on future projects).
Machines can create algorithms that produce automated translations that are mostly accurate and helpful, but anyone who can speak two languages and has tried Google Translate can agree that these translations are far from perfect, they will still need a real person to do a final editing. Without the creative process infused into the actual translation by the translator, the end result will be dull, lack soul and rhythm, sound unnatural, and definitely not pass as native speech.
In the end, every translator’s final translation will have his or her personal tone because humans can’t help but “create” elements of it… which makes it an “art” form.