Hello Rajesh,
Arabic language is supported in WebI 4.1. Right to left text alignment will work in Rich client and Applet interface and NOT in HTML when product locale is in Arabic. So while installing you have to choose language as Arabic. Check below document for details.
http://blasthemy.com/sap/TechEd13/1_Session_PDFs/EA/EA203/EA203.pdf
switching to Arabic language will not switch calendar to Islamic calendar. I am not sure if Webi supports Islamic calendar. Please check with SAP to confirm it or someone here will clarify on this. With ABAP code you can convert islamic date into gregorian date in back end system. Not sure if it will be useful in your scenario.
Regards,
Nikhil Joy