After updating to OS X 10.3.3, Safari's contextual menu would replace "Save Image As...", "Copy (Image or Link) to Clipboard", and others with the text "localized strings not found." Also, I was unable to login to password-protected Web sites (that used .htaccess files). WebKit is affected too, and you can test this by launching the Help Viewer and control-clicking on any image.
After some online research, I discovered many others experiencing the same problem after updating to 10.3.4. The fix that worked for me was to reinstall the 10.3.4 Combo Updater and restart. Voilá! It works!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040616150138872