Instead of 7 specific languages, I'd give you 7 categories:
A systems language, like C, C++. A managed language, like Java, C#. A weakly typed language, like Python, Lua. A web-server centric language, like PHP, Ruby. An automation language, like Bash, Batch. A functional language, like Erlang, Haskell. A domain-specific language, like SQL, Mathematica.
There is a book called "Seven Languages in Seven Weeks" ...
Ogre. OSG is a pain in the ass to use. Very cluttered API and almost no documentation. The vast majority of the methods isn't documented at all.
If you know OpenGL then OSG is straight forward to use and its documentation are the examples as well as the standard opengl documentation. But yes for getting a game fast up and running OGRE is the choice.
That depends for what?
I would argue for OSG if you need rending across network and good support for OpenGL ES or very good support for multi threaded rendering.
But if you want more then a graphics engine, go for Ogre.