Hi,
I am pretty sure that Arabic text does get filled into the fields. The problem is that a lot of PDF viewers don’t render form data correctly. There are a lot of different kinds of bugs. What you are experiencing is one such bug.
There is a workaround. It requires that the PDF software that fills in the form generate an ‘appearance value’ for the form field. Unfortunately, my current software stack does not do this.
I am working on switching to a different software stack that does generate the appearance value for the forms, however, the new version is not ready for use yet.
Unfortunately, there is no fix for your issue at the moment. I’m sorry for any inconvenience this has caused you.