Backing up files and directories is easily achieved using a standard shell like Bash. Bash can find and copy files using commands like find and ditto. You could use other languages, but Bash is the simplest and most universal solution.
A web content management system is a complex piece of software, and demands a powerful scripting language. Python or Perl would be most appropriate for this purpose. The object-oriented features of Python would make it particularly attractive for building such an advanced system.
AppleScript wins this one hands down. It is the only scripting language that allows you to directly access data in applications like iPhoto, Address Book, and Mail.