convert file to utf8

function convert_to_utf8_recursively($dat)
{
    if (is_string($dat))
        return utf8_encode($dat);
    if (!is_array($dat))
        return $dat;
    $ret = [];
    foreach ($dat as $i => $d)
        $ret[$i] = self::convert_to_utf8_recursively($d);
    return $ret;
}