In our globalized world, more and more economies are becoming interdependent on each other. As a result, it has become imperative for companies to adapt to different cultures, people, and languages. In web design too, support for localization has become almost mandatory.
In fact, nowadays, when a prospective client does a keyword search for your product or service, they are searching in their own native language. If your website does not have the keyword published in their language, your search rank will surely suffer.
Top 10 Internet Users by Language (2011)
All said and done, English is no longer the dominant language on the web for eCommerce, especially in the emerging markets of Asia-Pacific and South America.