Sorry for adding the guide so late, been a little busy.
Adding Arabic support usually involves patching both Framework.jar and libwebcore.so files.
I found that patching libwebcore.so file causes crashes with the default browser, Gmail and Google reader. I've tried to patch the libwebcore.so manually and automatically using the method mentioned in this website :
http://blog.devasque.com/?page_id=11
But it does not work. Also, Default android browser is buggy at best, so using Opera Mini which supports Arabic won't be a problem.
1-First you need to have your device rooted with any of the methods here in XDA. Also make sure you have the 1.1 version as I didn't try to add Arabic to 1.0 version.
2-Make a backup of your whole system using the method found here just in case:
http://xdaforums.com/showthread.php?t=1142983
You can also try CWM backup, but I didn't try it.
3-Download this file:
https://rapidshare.com/files/2199861553/Arabic_Support_for_NST.rar
Extract it, and Using Root Explorer copy the file framework.jar for /system/framework/, and copy the libandroid_runtime.so and libicuuc-arabic.so to /system/lib/
System might restart during copying files, try again after system has restarted.
Or
You can try the CWM flashable zip file:
https://rapidshare.com/files/1924264561/flashable_cwm_framework.zip
copy the zip file to sd, boot in CWM, flash file from sd.
Didn't try the CWM flashable file, but I don't find any reason why it won't work.
3- Add the Arabic font, I use the DejaVuSans. Can be found here :
https://rapidshare.com/files/2414620233/DroidSansFallback.rar
Using Root Explorer copy the file to /system/fonts/ overwriting the exiting file. Reboot.
If you don't like the font, use any other Arabic Enabled DroidSansFallback.
All credits go to madmack.