protected function load_deprecated_strings() {
        global $CFG;

        if ($this->cacheddeprecated !== null) {
            return $this->cacheddeprecated;
        }

        $this->cacheddeprecated = array();
        $content = '';
        $filename = $CFG->dirroot . '/lang/en/deprecated.txt';
        if (file_exists($filename)) {
            $content .= file_get_contents($filename);
        }
        foreach (core_component::get_plugin_types() as $plugintype => $plugintypedir) {
            foreach (core_component::get_plugin_list($plugintype) as $pluginname => $plugindir) {
                $filename = $plugindir.'/lang/en/deprecated.txt';
                if (file_exists($filename)) {
                    $content .= "\n". file_get_contents($filename);
                }
            }
        }

        $strings = preg_split('/\s*\n\s*/', $content, -1, PREG_SPLIT_NO_EMPTY);
        $this->cacheddeprecated = array_flip($strings);

        return $this->cacheddeprecated;
    }