Making a theme multilingual by adding a custom taxonomy to posts and pages called “Languages”?

2 comments

1. The Pro: You can reuse native WP code.

   Contra: You have to write your own taxonomy selector to avoid posts tagged with more than one language. The plugin Posts 2 Posts from @scribu should guide you to a more flexible approach.

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2. I was facing a similar dilemma this week, and ended up creating a solution which I thought you might find useful.

   I personally dislike the use of taxonomies for this purpose. I think the only pro is that it’s already built-in, and maybe it gives you a good out-of-the-box permalink structure, but it feels like a corruption of the taxonomies original purpose.

   My approach is fairly self-sufficient and uses postmeta to store translations. All you would have to do to filter posts which have translations is to check for _translate_content_{$lang} post meta (e.g. _translate_content_fr_FR). I haven’t yet coded the front-end parts, but that should vary a lot according to what you want to do in your theme.

   Code is commented, but let me know if there is anything that’s not clear.

   Note: I do this for pages only, but it should be easy to add posts to it as well. Also, keep in mind that I haven’t tested this with revisions, which I don’t use.

   # Create a list of available languages for translation;
   # Note: the keys are WordPress locale codes, so we can easily integrate it
   function my_available_languages() {
       return array(
           'en_US' => array(
               'value' => 'en_US',
               'label' => 'English (U.S.)',
           ),
           'fr_FR' => array(
               'value' => 'fr_FR',
               'label' => 'Français',
           ),
           'de_DE' => array(
               'value' => 'de_DE',
               'label' => 'Deutsch',
           ),
           'es_ES' => array(
               'value' => 'es_ES',
               'label' => 'Español',
           ),  
       );
   }
   
   # Allow translations
   add_action('current_screen', 'enable_translation');
   function enable_translation($screen) {
       # Only process translations for existing posts
       if(in_array($screen->post_type, array('page')) && $screen->base == 'post' && $screen->action != 'add') {
           if(isset($_GET['translate']) && array_key_exists($_GET['translate'], my_available_languages())) {
   
               # Load translated fields instead of the original post content
               add_filter('title_edit_pre', create_function('', 'return get_translate_field("title", "' . $_GET['translate'] . '");'));
               add_filter('content_edit_pre', create_function('', 'return get_translate_field("content", "' . $_GET['translate'] . '");'));
               add_filter('excerpt_edit_pre', create_function('', 'return get_translate_field("excerpt", "' . $_GET['translate'] . '");'));
   
               # Add hidden field so that 'translate' param persists
               add_action('submitpage_box', 'doing_translate_hidden_field');
   
               # Remove unnecessary metaboxes, which are not pertinent for translation
               add_action('add_meta_boxes', 'redo_metaboxes_on_translate', 99, 2);
   
               # Reduce the layout columns options
               add_filter('screen_layout_columns', 'screen_layout_columns_translate_page');
               function screen_layout_columns_translate_page($columns) {
                   $columns['page'] = 1;
                   return $columns;
               }
   
               # Set one column default layout on dashboard
               add_filter('get_user_option_screen_layout_page', create_function('', 'return 1;'));
   
               # Notify user that he is viewing a translated version
               add_action('admin_notices', 'doing_translation_notification');
           }
       }
   }
   
   add_action('add_meta_boxes', 'add_translation_metabox', 98, 2);
   function add_translation_metabox($post_type, $post) {
       # Optional: add this box conditionally
       $types = array('page');
       if(in_array($post_type, $types)) {
           foreach($types as $type) {
               add_meta_box('translate_mgmt', __('Translations', 'text_domain'), 'output_translate_mgmt_metabox', $type, 'side', 'low');   
           }
       }
   }
   
   # Output a list of links of available languages for translation
   function output_translate_mgmt_metabox() {
       global $post;
       $default = 'en_US';
       # get_edit_post_link will return a filtered admin_url link, so we must attempt to remove the translate param, in case it's already added
       $link = remove_query_arg('translate', get_edit_post_link($post->ID));
       echo('<ul>');
       foreach(my_available_languages() as $code => $lang) {
           $href = $code != $default ? add_query_arg(array('translate' => $code), $link) : $link;
           echo('<li><a href="' . $href . '">' . $lang['label'] . '</a></li>');
       }
       echo('</ul>');
   }
   
   function redo_metaboxes_on_translate($post_type, $post) {
   
       # Add alternative save metabox
       add_meta_box('translate_save', __('Save', 'text_domain'), 'output_translate_save_metabox', 'page', 'normal', 'low');
   
       # Remove unnecessary metaboxes
       remove_meta_box('slugdiv', 'page', 'normal');   
       remove_meta_box('authordiv', 'page', 'normal');
       remove_meta_box('postcustom', 'page', 'normal');
       remove_meta_box('commentsdiv', 'page', 'normal');
       remove_meta_box('commentstatusdiv', 'page', 'normal');  
       remove_meta_box('submitdiv', 'page', 'side');
       remove_meta_box('pageparentdiv', 'page', 'side');   
       remove_meta_box('revisionsdiv', 'page', 'side');
       remove_meta_box('trackbacksdiv', 'page', 'side');
       remove_meta_box('postimagediv', 'page', 'side');
   }
   
   # Output a simpler, 'just save' button, so translators are not confronted with too many options that affect main post
   function output_translate_save_metabox() { ?>
       <input type="submit" class="ui_button big save" value="<?php _e('Save', 'text_domain'); ?>" />
   <?php
   }
   
   # Add a notice to the user (like the update WordPress nag) so that it's clear that he is currently viewing a translated version
   function doing_translation_notification() {
       global $post;
       $langs = my_available_languages();
       echo "<div class='update-nag'>" . sprintf(__('You are currently translating the page "%s" into %s.', 'text_domain'), get_the_title($post->ID), $langs[$_REQUEST['translate']]['label']) . "</div>";
   }
   
   # Add hidden input which will add 'translate' to the $_POST object, thus allowing it to persist after redirection
   # Note: I use jQuery to remove the slug below the title, but it's optional, I guess
   function doing_translate_hidden_field() { ?>
       <input type="hidden" name="translate" value="<?php echo($_REQUEST['translate']); ?>" />
       <script type="text/javascript">
           jQuery(function($){
               $('#edit-slug-box').remove();
           });
       </script>
   <?php
   }
   
   # Return translated content
   function get_translate_field($field, $lang) {
       global $post;
       return get_post_meta($post->ID, '_translate_' . $field . '_' . $lang, true);    
   }
   
   add_action('admin_init', 'add_translation_content_filters');
   function add_translation_content_filters() {
       $fields = array('title', 'content', 'excerpt'); // As named in filters, not on their form inputs / db
       foreach($fields as $field) {
           add_action($field . '_save_pre', create_function('$cont', 'return update_translation_on_save($cont, "' . $field . '");'), 1, 1);
       }
   }
   
   # If doing translation, update pertinent post meta instead of post row on database
   function update_translation_on_save($content, $field) {
       $db_fields = array(
           'title' => 'post_title',
           'content' => 'post_content',
           'excerpt' => 'post_excerpt',
       );
       global $post;
       if(is_object($post) && isset($_REQUEST['translate'])) {
           update_post_meta($post->ID, '_translate_' . $field . '_' . $_REQUEST['translate'], $content);
           $content = $post->{$db_fields[$field]};
       }
       return $content;
   }
   
   # Function to add 'translate' param to a given URL (to be used with filters) 
   function add_translate_param($link) {
       # Optional: don't add 'translate' on pages which are not for content management
       if(strpos($link, 'post.php') === false && strpos($link, 'edit.php') === false) {
           return $link;
       }
       return add_query_arg(array('translate' => isset($_REQUEST['translate']) ? $_REQUEST['translate'] : ''), $link);
   }
   
   if(isset($_REQUEST['translate'])) {
       # Make 'translate' URL parameter persistent 
       add_filter('admin_url', 'add_translate_param');
       add_filter('wp_redirect', 'add_translate_param');
       # Add 'doing_translate' body class
       add_filter('admin_body_class', create_function('$c', '$c .= " doing_translate"; return $c;'), 99);
   }
   

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