private function get_plural_forms() {
        // lets assume message number 0 is header
        // this is true, right?
        $this->load_tables();

        // cache header field for plural forms
        if (!is_string($this->pluralheader)) {
            if ($this->enable_cache) {
                $header = $this->cache_translations[""];
            }
            else {
                $header = $this->get_translation_string(0);
            }
            if (preg_match("/plural\-forms: ([^\n]*)\n/i", $header, $regs))
                $expr = $regs[1];
            else
                $expr = "nplurals=2; plural=n == 1 ? 0 : 1;";
            $this->pluralheader = $expr;
        }
        return $this->pluralheader;
    }