I am doing exactly this at the moment, i.e. trying to get some working knowledge of different languages and environments at the same time.
The method. Think about an example application that is not too complex (e.g. not a complete GUI application) but also not trivial (more complex than "Hello world"), something that requires around 5000-1000 lines of code (but you should choose what is the appropriate size for you), and using different techniques (abstract data types, packages, inheritance, memory management, generic programming, whatever) that you want to explore.
When you have defined your example application, write down an approximate design / sketch of how you want to implement it.
Then, just implement it, in all the chosen languages, following the same overall design.
The process of getting the example application to compile and run without bugs will guide you to acquire knowledge about each language or framework (books, API documentation, compiler switches, etc) in a very practical, efficient, and focused way.
I am doing this experiment with C, C++, Ada, Lisp, and a few other languages and I am really learning a lot.
Just my 2 cents.