What comes up with logcat?
Make sure it was built for Android 2.1.
You often can't just swap libraries like that, especially core libraries like libwebcore. Performing a device data wipe sometimes helps as well.
In my experience, to add Arabic support, you need to just change the font files for the characters to show up. To get them to link up, you need to modify the libraries. The files used to be hosted at http://code.google.com/p/arabicandroid/ but they were taken down at one point.
Your best bet if you are not comfortable with recompiling is to try to swap a libwebcore from a SIMILAR device such as the Nexus One. Make sure it is taken from one made for Android 2.1. If you can find a mirror of that ROM, those files might just work.
According to this: Arabic/Persian Support on Éclair Stock Rom - xda-developers
You might need 3 files, not just libwebcore