As I understood it, you want to create the CMS yourself.
Like the poster before me said, there isn't a favorable language (imo). There are plenty of web frameworks that could give you a "big" hand in creating a CMS. You could create everything from scratch, though that might seem a bit much (unless it is your goal to do just that).
So, I would do some research on web frameworks. There are gazillions of web frameworks out there, like CakePHP, Zend (PHP), Symfony2 (PHP), Django (written in Python), Flask (Python), Pyramid (Python), Ruby on Rails (written in Ruby), Sinatra (Ruby), and a plethora of other web frameworks to choose from.
It's more important to determine what you actually want to do, what criteria you've set and then pick what meets those criteria best.