When hiring a website translator, what qualifications do you look for?

When hiring a website translator, what qualifications do you look for?

When hiring a document or page translator, I would want to ensure the person was a native speaker of the language in which the site was being translated into and could easily convert English into a specific language. This person should be fluent in the spoken and written word as well as a good writer in their own language, so they could polish up the written work to be visually appealing to those reading the finished product.