Hi there.

I have a somewhat average programming background (some OOP in Java and C++, python, scheme) and intend to run an imageboard in Arabic. What do I have to learn and which packages do you suggest I choose?

You should learn Arabic first.

After that: go with Wakaba. :)
You'll need MySQL, Perl, and the MySQL bindings for Perl (perl-dbi and perl-dbd-mysql). It'd be quite helpful to know how to write Perl, but you really don't need to, as it's rather straightforward to figure out what stuff needs changed.

For translating: copy strings_en.pl to strings_ar.pl or whatever it is (name doesn't really matter), and change the require in both wakaba.pl and captcha.pl to point to the right file. Then edit your include/rules.html as well, hit up wakaba.pl from a browser and it Should Work.

these guys have a board running in hebrew
http://www.animeholic.net/i/futaba.php
maybe they can help you. dont necessarily tell them that you want to run a board in arabic.
also http://www.chankom.org/ used to have arabic imageboards, but now they're gone. maybe you can contact them via their whois info.