In order to get closer to users, large web stores usually support several store views based on specific language. By default, the same URL in Magento can display different locale interface which is, obviously, a bad thing for search engines and SEO. Using separate domain names for that matter does not always suite shop owners, and to say more, is not worth it.
Alternatively, it is possible, and recommended, to use the Magento default setting "Add Store Code to Urls". However, there is a...