What languages do I need to know to create a blog with a control panel?

Full-Stack Javascript will definitely point you in the right direction. I believe it covers the basics of Javascript, as well as Node and Mongo. Eventually they'll help you handle basic user authentication (login/out).

They don't go into how you would specifically make a blog - but if you go through the course you should get a good feeling as to the direction you need to go. User authentication is probably the most complex piece of a blog (which parts of the site, like the control panel, do you show - and to whom?), and they walk you through that.

At the very least, once you get through those courses you'll know enough to know what you're lacking, and know what to do and where to go to start researching. Then, of course, you also have this community (and the various other awesome communities like StackOverflow) to pull from :)