Tolga,

I'm going to risk several demerits here, and recommend that you look at
Python first, and Ruby second, for the following reasons:

1. Python was initially funded, designed, and documented in large part
as a "teaching" language. The syntax is *extremely* consistent, as are
the core libraries.

2. The free, online documentation for Python is absolutely without
peer. Working just from the main tutorial and langauge reference on the
main Python website, you should have no trouble getting up to speed on
the language.

3. Python still has a more substantial presence in both CS and the
natural sciences, which means more (and somewhat higher-quality)
libraries and books covering the techniques and tools you will need for
AI work. Peter Norvig, very highly-respected AI researcher and
instructor, has even translated his code from "AI: A Modern Approach"
from Lisp to Python.

4. In my experience, the GUI libraries for Python are simply more
mature, better documented, (there's that word again!) and more widely
used that the equivalents for Ruby. If you want rich client interfaces,
using Python will make your life easier.

That being said, the languages are really more alike in capabilities
than different. Also, even with the recent rise of Rails into
popularity, it has been my experience that the Ruby community is
absolutely wonderful to work with; it is seldom you will see a question
be ignored or the asker scorned, even in high-volume channels like this
newsgroup.

Regardless of which language you choose, I wish you the best of luck.

-Lennon
http://rcoder.net/