Which language is majorly used to make treehouse website?

I don't think it's really fair to call it a CMS, even if the definition technically applies. Treehouse is pretty much all custom Rails code - the forums, code challenges, quizzes, and video delivery are all hand-made in our factory in Taiwan.

We could've used an off-the-shelf product or library to build the site around, certainly, but while that kind of thing helps with getting a product launched quickly, it also severely hampers your ability to iterate and improve. Having everything based off of our custom code has allowed us to make a lot of the changes you've seen to Treehouse since its launch very quickly and easily compared to what we would've needed if we'd been, say, a bastardized WordPress or (shudder) Joomla setup.

Hope that answers your question Johan Hernández - I'm watching the thread if you (or anyone else) have any followups :)

We definitely use plugins, though :) The Gemfile for Treehouse is 145 lines long - although most of the stuff we do involves creating custom code, we also take full advantage of any existing libraries/plugins that do what we want/need. One of the great advantages of using Ruby is the access you have to the Ruby ecosystem, which exhibits a thriving culture of sharing code. In fact, there are a few libraries that we wrote here at Treehouse that we've open-sourced and released as ruby gems.

So I wouldn't be too hard on using plugins. For any sufficiently complicated site you'll need to branch out and do your own custom development, but learning to work with plugins and other open-source libraries is a pretty solid start.