This issue came up with improvements to GDAL's handling of encoding. It was discussed here on the qgis maillist. There are some suggested workarounds in that dicussion. I'm sure a permananet solution will appear soon, but what I found solves the problem fro now is the suggestion by Even Rouault:
First you need to have all the text attributes in your shapefile encoded as UTF-8. THen add to the batch file that starts QGIS (usually OSGEO4W\bin\qgis.bat) one line to set an enviroment variable:
With that, you can then save text strings (in my case in hebrew, but I suppose Arabic will be the same) without it getting turned into question marks.