in case your string contain Arabic char, ZipArchive::addFromString will show it in wrong format char.
in this case you have to change your string coding from Unicode to Windows-1256 code
$filetxt = iconv('utf-8','CP1256',$filetxt);
$zip = new ZipArchive;
$zipFName = "Tmp.zip";
if ($zip->open($zipFName, ZipArchive::CREATE) === TRUE)
{
$zip->addFromString($fileName . '.csv', $filetxt);
$zip->close();
}