There are various ways to do this depending on the site set up like say Joomla has "Extensions >> Language Manager", with "System – Language Filter" Drupal something else > https://drupal.org/project/i18n with https://drupal.org/project/variable and WP you can use various methods > http://codex.wordpress.org/Multilingual_WordPress and there are of course many other ways to do all things as there nearly always is.