Magento 2 UPS Shipping Labels Arabic Characters

when I print shipping label of UPS shipment in UPS, I get all arabic characters like that: ??????
I have read that’s because of ZEND_PDF, and I should install TCPDF, but I don’t know how to replace it, where is that module that create the shipping label?
I think it’s coming as image from UPS.com not generated in the magento.

and this is screenshot from UPS.com website, the same arabic characters are not written correctly:

I found this file:
vendor/magento/module-shipping/Controller/Adminhtml/Order/Shipment/PrintLabel.php

where I can edit the file name from here:

 return $this->_fileFactory->create(
 'ShippingLabel(' . $shipment->getIncrementId() . ').pdf',
  $pdfContent,
  DirectoryList::VAR_DIR,
  'application/pdf'
  );

and the contents ( can add to the pdf file content after it’s end ) but can’t edit the content itself .
where it’s $pdfContent coming from

        $shipment = $this->shipmentLoader->load();
        $labelContent = $shipment->getShippingLabel();

but I couldn’t reach to where is getShippingLabel() exactly and where is that label coming from.