private static function utf8ToCharset(string $content, string $encoding = null): string
    {
        if ($encoding !== 'UTF-8' && $encoding !== null) {
            return \mb_convert_encoding($content, $encoding, 'UTF-8');
        }

        return $content;
    }
private static function utf8ToCharset(string $content, string $encoding = null): string
    {
        if ($encoding !== 'UTF-8' && $encoding !== null) {
            return \mb_convert_encoding($content, $encoding, 'UTF-8');
        }

        return $content;
    }
private static function utf8ToCharset ( string $ content , string $ encoding = null ) : string { if ( $ encoding !== 'UTF-8' && $ encoding !== null ) { return \ mb_convert_encoding ( $ content , $ encoding , 'UTF-8' ) ; } return $ content ; }
Convert a UTF8 string to the specified encoding.

@param string      $content  String to decode
@param null|string $encoding Target encoding

@return string
Convert a UTF8 string to the specified encoding .