Must-Use Plugin Not Available for String Scanning in Theme and Plugins Localization

Overview of the issue

Must-Use (MU) plugins are not available for string scanning under WPML > Theme and Plugins Localization page.

Workaround

Please, make sure of having a full backup of your site before proceeding.

• Open …/wp-content/plugins/wpml-string-translation/classes/menus/theme-plugin-localization-ui/class-st-plugin-localization-ui-utils.php file.
• Look for line 6.
• Replace:

  	/** @return array */
  	public function get_plugins() {
  		$plugins    = get_plugins();
  		$mu_plugins = wp_get_mu_plugins();
  
  		if ( $mu_plugins ) {
  			foreach ( $mu_plugins as $p ) {
  				$plugin_file             = basename( $p );
  				$plugins[ $plugin_file ] = array( 'Name' => 'MU :: ' . $plugin_file );
  			}
  		}
  
  		return $plugins;
  	}
  

• With:

  public function get_plugins() {
  	$plugins = get_plugins();
  	$mu_plugins = wp_get_mu_plugins();
  
  	if ( $mu_plugins ) {
  		foreach ( $mu_plugins as $p ) {
  			$plugin_file = basename( $p );
  			$plugins[ $plugin_file ] = array( 'Name' => 'MU :: ' . $plugin_file );
  		}
  
  		//Workaround
  		$folders = scandir(WPMU_PLUGIN_DIR);
  		$folders = array_diff($folders, array('.', '..'));
  		
  		foreach($folders as $folder) {
  			if (is_dir(WPMU_PLUGIN_DIR.'/'.$folder)) {
  				$plugin_file = basename( $folder );
  				$plugins[ $plugin_file ] = array( 'Name' => 'MU :: ' . $plugin_file );
  			}
  		}
  	}
  
  	return $plugins;
  }