How to convert English quotation marks to Chinese quotation marks in php

$test_string = 'this is a "test as" string juventus vs "napoli" is  b a bing match';
echo convertQuotToChinese($test_string);
 
function convertQuotToChinese($string) {
    $flag = false; //false显示开始的中文引号,true时显示结束的中文引号
    while(false !== ($i = strpos($string, '"'))) {
        $begin_string = substr($string, 0, $i);
        $end_string = substr($string, $i+1-strlen($string));
        $quot = $flag ? '”' : '“';
        $flag = !$flag;
        $string = $begin_string.$quot.$end_string;    
    }
    return $string;
}