public function setPluralForms($count, $rule)
    {
        if (preg_match('/[a-z]/i', str_replace('n', '', $rule))) {
            throw new \InvalidArgumentException('Invalid Plural form: ' . $rule);
        }
        $this->setHeader(self::HEADER_PLURAL, "nplurals={$count}; plural={$rule};");

        return $this;
    }