这里是函数，经过测试，运行良好.

Here is the function, tested and works fine.

注意: &bdquo 仅 应用在开头， &rdquo 只应用在字符串的末尾.(hsz 的解决方案不遵循该规则)

Note: the &bdquo applies only at the beginning, the &rdquo only at the end of an string. (hsz's solution isn't following that rule)

function germanquotes($text){
    $size = strlen($text);
    $i=0;
    $replace = array();
    $replace['one'] = array();
    $replace['two'] = array();
    while($i < $size)
    {
        if($text[$i] == '"')
        {
            if($text[$i-1] == " " || empty($text[$i-1]))
            {
                    $replace['one'][] = $i;
            }
            elseif($text[$i+1] == " " || empty($text[$i+1]))
            {
                $replace['two'][] = $i;
            }
        }

        $i++;
    }

    $y = 0;
    $it = 0;
    foreach($replace['one'] as $ghh)
    {
        $text = substr_replace($text, '&bdquo;', ($ghh+$y), 1);
        $y += 6;
        $it++;
    }

    $to=0;
    $i=1;
    $u=1;
    foreach($replace['two'] as $ghhd)
    {
        $text = substr_replace($text, '&rdquo;', ($ghhd-1+$to+((8*$i)-($u*1))), 1);
        $i++;
        $u +=2;
        $to +=6;
    }

    return $text;
}

测试:

echo(germanquotes('I am "glad" to write "functions" for "***" users'));