For what is worth, I suspect your file conversion (I meant on viewing) does not support right to left (Hebrew, Arabic,…) in pptx files.
Please share sample PPTX and code that you are using to view/render the document.
Using you .net MVC example, pptx. can not be uploaded from here. Interesting.
English sentence Google translated into Persian, Hebrew and Arabic.
image.png (8.7 KB)
Please upload sample PPTX to some cloud storage (e.g. Dropbox) and share its link here. We’ll then investigate the issue.