yii\filters\ContentNegotiator::isLanguageSupported PHP Метод

    protected function isLanguageSupported($requested, $supported)
    {
        $supported = str_replace('_', '-', strtolower($supported));
        $requested = str_replace('_', '-', strtolower($requested));
        return strpos($requested . '-', $supported . '-') === 0;
    }