There's no shortage of online translation tools and mobile apps, but Promt, a free online translator and dictionary, is one that translates large blocks of text accurately. The company manufactures desktop software for translating PDFs and larger documents, but this free web-based service is incredibly accurate and easy to use. You can copy and paste large blocks of text to translate, or use the website translator for an entire site; just enter the site's URL and desired start and finish languages. You can even set categories for greater accuracy; try "Travel," "Cars," "Sports," and more.
There's also a mobile version of the site should you need to translate on the go; Promt currently supports English, Spanish, French, Portuguese, Russian, and Italian.