I should not say multiple languages design, multiple languages feature is more appropriate.
The World Wide Web is not for english only anymore. More people who speak other than English has access to the Internet the same way other people access to the Internet. So why not build a website that support more than one languages?
The previous approach of the multiple language was to develop a site with one language. When it is finished, copy the entire content and put it under another folder best fit with the language itself and then translate the content word by word to the targeted language.
One problem quickly surface: The pain of update.
While we have more powerful computers and database driven website, to implement multiple languages website become much easier.
How much more visitors will there be when a website can serve more than one languages? It surely will be more.