Most probably json_decode have problem with arabic charactor. The arabic text should convert to utf-8.if after decode also the arabic text coming properly hope you will get the result.
@header('Content-Type: text/html; charset=utf-8');
$response="بسم الله الرحمن الرحيم";
$response= iconv('windows-1256', 'utf-8', ($response));
$string='{
"something": "'.$response.'"
}';
echo "Before Decode :";
var_dump($string);
echo "After Decode :";
$json=json_decode($string);
var_dump($json);