首先必须检测使用了什么编码。在解析RSS提要时(可能通过HTTP)，应该从Content-Type HTTP报头字段的字符集参数中读取编码。如果不存在，则从XML处理指令的encoding属性中读取编码。如果也没有，请使用规范中定义的UTF-8。

以下是我可能会做的:

I’d use cURL to send and fetch the response. That allows you to set specific header fields and fetch the response header as well. After fetching the response, you have to parse the HTTP response and split it into header and body. The header should then contain the Content-Type header field that contains the MIME type and (hopefully) the charset parameter with the encoding/charset too. If not, we’ll analyse the XML PI for the presence of the encoding attribute and get the encoding from there. If that’s also missing, the XML specs define to use UTF-8 as encoding.

$url = 'http://www.lr-online.de/storage/rss/rss/sport.xml';

$accept = array(
    'type' => array('application/rss+xml', 'application/xml', 'application/rdf+xml', 'text/xml'),
    'charset' => array_diff(mb_list_encodings(), array('pass', 'auto', 'wchar', 'byte2be', 'byte2le', 'byte4be', 'byte4le', 'BASE64', 'UUENCODE', 'HTML-ENTITIES', 'Quoted-Printable', '7bit', '8bit'))
);
$header = array(
    'Accept: '.implode(', ', $accept['type']),
    'Accept-Charset: '.implode(', ', $accept['charset']),
);
$encoding = null;
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_HEADER, true);
curl_setopt($curl, CURLOPT_HTTPHEADER, $header);
$response = curl_exec($curl);
if (!$response) {
    // error fetching the response
} else {
    $offset = strpos($response, "\r\n\r\n");
    $header = substr($response, 0, $offset);
    if (!$header || !preg_match('/^Content-Type:\s+([^;]+)(?:;\s*charset=(.*))?/im', $header, $match)) {
        // error parsing the response
    } else {
        if (!in_array(strtolower($match[1]), array_map('strtolower', $accept['type']))) {
            // type not accepted
        }
        $encoding = trim($match[2], '"\'');
    }
    if (!$encoding) {
        $body = substr($response, $offset + 4);
        if (preg_match('/^<\?xml\s+version=(?:"[^"]*"|\'[^\']*\')\s+encoding=("[^"]*"|\'[^\']*\')/s', $body, $match)) {
            $encoding = trim($match[1], '"\'');
        }
    }
    if (!$encoding) {
        $encoding = 'utf-8';
    } else {
        if (!in_array($encoding, array_map('strtolower', $accept['charset']))) {
            // encoding not accepted
        }
        if ($encoding != 'utf-8') {
            $body = mb_convert_encoding($body, 'utf-8', $encoding);
        }
    }
    $simpleXML = simplexml_load_string($body, null, LIBXML_NOERROR);
    if (!$simpleXML) {
        // parse error
    } else {
        echo $simpleXML->asXML();
    }
}

制定RSS提要的字符编码似乎很复杂。即使是普通的网页也经常忽略或谎报它们的编码。

因此，您可以尝试使用正确的方法来检测编码，然后退回到某种形式的自动检测(猜测)。

不带auto的Try

那就是:

mb_detect_encoding($text)

而不是:

mb_detect_encoding($text, 'auto')

更多信息可以在这里找到:mb_detect_encoding

你的编码看起来像是用UTF-8编码了两次;也就是说，从其他编码，转换成UTF-8，再转换成UTF-8。就好像您有ISO 8859-1，从ISO 8859-1转换为UTF-8，并将新字符串处理为ISO 8859-1，以便再次转换为UTF-8。

下面是你所做的一些伪代码:

$inputstring = getFromUser();
$utf8string = iconv($current_encoding, 'utf-8', $inputstring);
$flawedstring = iconv($current_encoding, 'utf-8', $utf8string);

你应该试试:

使用mb_detect_encoding()或任何您喜欢使用的方法来检测编码 如果是UTF-8，转换成ISO 8859-1，然后重复步骤1 最后，转换回UTF-8

这是假设在“中间”转换中使用ISO 8859-1。如果您使用的是Windows-1252，则转换为Windows-1252 (latin1)。原始源编码并不重要;你在有缺陷的第二次转换中使用的是。

以下是我对所发生事情的猜测;要用四个字节代替一个扩展的ASCII字节，您几乎没有其他办法。

德语也使用ISO 8859-2和Windows-1250(拉丁语-2)。

这个备备单列出了PHP中与UTF-8处理相关的一些常见注意事项: http://developer.loftdigital.com/blog/php-utf-8-cheatsheet

这个函数在字符串中检测多字节字符也可能是有帮助的(来源):

function detectUTF8($string) { return preg_match('%(?: [\xC2-\xDF][\x80-\xBF] # non-overlong 2-byte |\xE0[\xA0-\xBF][\x80-\xBF] # excluding overlongs |[\xE1-\xEC\xEE\xEF][\x80-\xBF]{2} # straight 3-byte |\xED[\x80-\x9F][\x80-\xBF] # excluding surrogates |\xF0[\x90-\xBF][\x80-\xBF]{2} # planes 1-3 |[\xF1-\xF3][\x80-\xBF]{3} # planes 4-15 |\xF4[\x80-\x8F][\x80-\xBF]{2} # plane 16 )+%xs', $string); }

此版本适用于德语，但您可以修改$CHARSETS和$TESTCHARS。

class CharsetDetector
{
    private static $CHARSETS = array(
        "ISO_8859-1",
        "ISO_8859-15",
        "CP850"
    );

    private static $TESTCHARS = array(
        "€",
        "ä",
        "Ä",
        "ö",
        "Ö",
        "ü",
        "Ü",
        "ß"
    );

    public static function convert($string)
    {
        return self::__iconv($string, self::getCharset($string));
    }

    public static function getCharset($string)
    {
        $normalized = self::__normalize($string);
        if(!strlen($normalized))
            return "UTF-8";
        $best = "UTF-8";
        $charcountbest = 0;
        foreach (self::$CHARSETS as $charset)
        {
            $str = self::__iconv($normalized, $charset);
            $charcount = 0;
            $stop = mb_strlen($str, "UTF-8");

            for($idx = 0; $idx < $stop; $idx++)
            {
                $char = mb_substr($str, $idx, 1, "UTF-8");
                foreach (self::$TESTCHARS as $testchar)
                {
                    if($char == $testchar)
                    {
                        $charcount++;
                        break;
                    }
                }
            }

            if($charcount > $charcountbest)
            {
                $charcountbest = $charcount;
                $best = $charset;
            }
            //echo $text . "<br />";
        }
        return $best;
    }

    private static function __normalize($str)
    {
        $len = strlen($str);
        $ret = "";
        for($i = 0; $i < $len; $i++)
        {
            $c = ord($str[$i]);
            if ($c > 128) {
                if (($c > 247))
                    $ret .= $str[$i];
                elseif
                    ($c > 239) $bytes = 4;
                elseif
                    ($c > 223) $bytes = 3;
                elseif
                    ($c > 191) $bytes = 2;
                else
                    $ret .= $str[$i];

                if (($i + $bytes) > $len)
                    $ret .= $str[$i];
                $ret2 = $str[$i];
                while ($bytes > 1)
                {
                    $i++;
                    $b = ord($str[$i]);
                    if ($b < 128 || $b > 191)
                    {
                        $ret .= $ret2;
                        $ret2 = "";
                        $i += $bytes-1;
                        $bytes = 1;
                        break;
                    }
                    else
                        $ret2 .= $str[$i];
                    $bytes--;
                }
            }
        }
        return $ret;
    }

    private static function __iconv($string, $charset)
    {
        return iconv ($charset, "UTF-8", $string);
    }
}