Change locale manually at runtime?

3 comments

1. I’m trying to do a similiar thing, and the experts on the wp-hackers mailing list (Otto, Nacin) told me this:

   Don’t try to change WPLANG, you can’t change a define’d constant.
   Instead, change the global $locale, or put a filter on ‘locale’.

   So the best solution is to apply a filter on the ‘locale’ global variable. The only way to do that is by creating a custom plugin. If you put the following piece of code into your functions.php file, it won’t work properly because it will run too late in the WP loading sequence.

   Your plugin could look like this (I’m just reusing the URI testing part from OneTrickPony, you can replace it with another conditional testing method):

   <?php
   /*
   Plugin Name: Change locale at runtime
   Plugin URI: http://wordpress.stackexchange.com/questions/49451/change-locale-at-runtime
   */
   
   function wpsx_redefine_locale($locale) {
       // run your tests on the URI
           $lang = explode('/', $_SERVER['REQUEST_URI']);
           // here change to english if requested
           if(array_pop($lang) === 'en'){
             $locale = 'en_US';
           // otherwise stick to your default language
           }else{
             $locale = 'gr_GR';
           }
       return $locale;
   }
   add_filter('locale','wpsx_redefine_locale',10);  
   ?>
   

   I hope this can help anyone!

   A few more warnings (quoting Andrew Nacin), regarding the cost in terms of performance when switching the locale:

   It is possible to “switch out” a locale after the default locale is
   loaded, but I would advise against that as it is inefficient, unless
   your default language is English, in which case it is not so bad.

   Default textdomain files are loaded after plugins_loaded and
   setup_theme, but before the theme is loaded and before
   after_setup_theme fires. Loading English then re-loading the
   textdomain into German on the init hook would be fine,
   performance-wise, as English has no mo files. But loading Spanish by
   default then switching to German would not.

   See http://codex.wordpress.org/Plugin_API/Action_Reference for useful info about the loading sequence.

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2. I don’t know if it’s possible to do this within a plugin, because of the constants WP requires defined before a certain point, but check for the requested language in wp-config.php and define the necessary constant:

   // split URI
   $lang = explode('/', $_SERVER['REQUEST_URI']);
   
   // here change to english if requested
   if(array_pop($lang) === 'en'){
     define('WPLANG', 'en_US');
   
   // otherwise stick to your default language
   }else{
     define('WPLANG', 'gr_GR');
   }
   

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3. At first, ensure that your desired locale is in a list (under “has a language pack“). If confirmed, then use such code:

   //set desired locale
   add_filter( 'locale', function($locale) {
       if ( !is_admin() ) 
           $locale = "zh_TW";
       return $locale;
   });
   

   If you haven’t chosen that language in WP dashboard, then you might need to use installer hook programatically:

   //check if it's not install, then install
   add_action('wp', 'my_locale_implemention');
   function my_locale_implemention()
   {
       $my_locale = get_locale();  //get_user_locale
       if ( !empty($my_locale) && !in_array( $my_locale, get_available_languages() ) ) {
           require_once( ABSPATH . 'wp-admin/includes/file.php' );
           require_once( ABSPATH . 'wp-admin/includes/translation-install.php' );
           $language = wp_download_language_pack( $my_locale );
           if ( $language ) {
               if(empty($_POST)) header("location: ".$_SERVER['REQUEST_URI']); exit; //reload page
           }
       }
   }
   

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