We build websites to get our messages out to the whole world, so why do we write them in English only? If your audience is spread across different language groups, WPML can help to deliver your website to them in their language.
Translation is always a big job, but WPML at least makes it easy to organise, working straight out of the box for standard blogs, and powerful enough to be customised for fully featured websites. WPML is a premium priced plugin, but they do offer free lifetime subscriptions for registered not-for-profits
Here are some websites harnessing WPML to translate whole libraries, as well as just individual posts: