public function add_texts($dir, $add2client = false)
    {
        $domain = $this->ID;
        $lang   = $_SESSION['language'];
        $langs  = array_unique(array('en_US', $lang));
        $locdir = slashify(realpath(slashify($this->home) . $dir));
        $texts  = array();

        // Language aliases used to find localization in similar lang, see below
        $aliases = array(
            'de_CH' => 'de_DE',
            'es_AR' => 'es_ES',
            'fa_AF' => 'fa_IR',
            'nl_BE' => 'nl_NL',
            'pt_BR' => 'pt_PT',
            'zh_CN' => 'zh_TW',
        );

        // use buffering to handle empty lines/spaces after closing PHP tag
        ob_start();

        foreach ($langs as $lng) {
            $fpath = $locdir . $lng . '.inc';
            if (is_file($fpath) && is_readable($fpath)) {
                include $fpath;
                $texts = (array)$labels + (array)$messages + (array)$texts;
            }
            else if ($lng != 'en_US') {
                // Find localization in similar language (#1488401)
                $alias = null;
                if (!empty($aliases[$lng])) {
                    $alias = $aliases[$lng];
                }
                else if ($key = array_search($lng, $aliases)) {
                    $alias = $key;
                }

                if (!empty($alias)) {
                    $fpath = $locdir . $alias . '.inc';
                    if (is_file($fpath) && is_readable($fpath)) {
                        include $fpath;
                        $texts = (array)$labels + (array)$messages + (array)$texts;
                    }
                }
            }
        }

        ob_end_clean();

        // prepend domain to text keys and add to the application texts repository
        if (!empty($texts)) {
            $add = array();
            foreach ($texts as $key => $value) {
                $add[$domain.'.'.$key] = $value;
            }

            $rcube = rcube::get_instance();
            $rcube->load_language($lang, $add);

            // add labels to client
            if ($add2client && method_exists($rcube->output, 'add_label')) {
                if (is_array($add2client)) {
                    $js_labels = array_map(array($this, 'label_map_callback'), $add2client);
                }
                else {
                    $js_labels = array_keys($add);
                }
                $rcube->output->add_label($js_labels);
            }
        }
    }