In many instances, Microsoft applications interpret the need for RTL
rendering from the characters used.
Would it be possible for you to create a pptx with Arabic text with POI and
then use Powerpoint to view it?
If there any rendering issues, fix it with Powerpoint. Then, send the POI
team the 2 versions of the pptx (one generated by POI) and the one with
rendering fix. We can then reverse engineer any changes that need to be made
to POI to support this.