One of the most widespread options to create a multi-language site with WordPress is to use the qTranslate plugin, wich works pretty well and it’s free. Perhaps the most sensitive aspect of multilingual sites is URL translation, since it affects website’s information architecture and search engine optimization (SEO).
Google XML Sitemaps v3 for qTranslate doesn’t work with Qtranslate Slug
Google XML Sitemaps v3 for qTranslate doesn’t work with Qtranslate Slug