Removing category base

Hello,

This is not that simple… In order to do this with multilanguage you need to add rewrite rules for every translation of every categories. This snippet should do it:

add_filter('category_rewrite_rules', function($rules) {
  global $wp_rewrite, $sublanguage_admin;
  
  if (isset($sublanguage_admin)) {
    
    $terms = get_terms(array(
      'taxonomy' => 'category',
      'hide_empty' => false
    ));
  
    $term_slugs = array();
  
    foreach ($sublanguage_admin->get_languages() as $language) {
    
      if ($sublanguage_admin->is_sub($language)) {
    
        $taxonomy_slug = $sublanguage_admin->translate_taxonomy('category', $language, 'category');
    
        foreach ($terms as $term) {
      
          $term_slugs[] = $sublanguage_admin->translate_term_field($term, 'category', 'slug', $language, $term->slug);
      
        }
    
        $term_slug_group = implode('|', $term_slugs);
    
        $rules["({$term_slug_group})/{$wp_rewrite->pagination_base}/?([0-9]{1,})/?$"] = 'index.php?sublanguage_slug='.$taxonomy_slug.'&category_name=$matches[1]&paged=$matches[2]';
        $rules['('.$term_slug_group.')/?$'] = 'index.php?sublanguage_slug='.$taxonomy_slug.'&category_name=$matches[1]';
    
      }
    
    }
    
  }

  return $rules;

}, 11);

Then you can fix the category links this way:

add_filter('term_link', function($termlink, $term, $taxonomy) {
  global $wp_rewrite, $sublanguage;
  
  $permastruct = $wp_rewrite->get_extra_permastruct($taxonomy);
  
  if (isset($sublanguage) && $permastruct) {
  
    $translated_tax = $sublanguage->translate_taxonomy($taxonomy, null, $taxonomy);
    $translated_slug = $sublanguage->translate_term_field($term, $taxonomy, 'slug');
  
    $termlink = str_replace(array($taxonomy, "%$translated_tax%"), array($translated_tax, $translated_slug), $permastruct);
    $termlink = home_url(user_trailingslashit($termlink, 'category'));
    
  }
  
  return $termlink;
}, 11, 3);

Tell me if it works. Don’t forget to refresh your permalinks!