"how to keep the chinese or other foreign language as they are instead of converting them into codes?" Code Answer

DOMDocument seems to convert Chinese characters into codes [...]. How can I keep the Chinese or other foreign language as they are instead of converting them into codes?

$dom = new DOMDocument();
$dom->loadHTML($html);

If you're using the loadHTML function to load a HTML chunk. By default DOMDocument expects that string to be in HTML's default encoding (ISO-8859-1) however most often the charset (sic!) is meta-information provided next to the string you're using and not inside. To make this more complicated, that meta-information be be even inside the string.

Anyway as you have not shared the string data of the HTML and you have not specified the encoding, it's hard to tell specifically what is going on.

I assume the HTML is UTF-8 encoded but this is not signalled within the HTML string. So the following work-around can help:

$doc = new DOMDocument();
$doc->loadHTML('<?xml encoding="UTF-8">' . $html);

// dirty fix
foreach ($doc->childNodes as $item)
    if ($item->nodeType == XML_PI_NODE)
        $doc->removeChild($item); // remove hack
$doc->encoding = 'UTF-8'; // insert proper

It injects an encoding hint on the very beginning (and removes it after the HTML has been loaded). From that point on, DOMDocument will return UTF-8 (as always).