Lately, there were a lot of questions related to career planning and how to decide which languages to learn, how to learn new languages and so on. But I was thinking about a way, how do you will proof later that you're really learned something. Ok you can mentione it in your application for a job or in the interview, but by just stating that I was learning e.g. C++ at home, I don't think this will really be very sucessful.

So some suggested to create something (homepage, application, whatsoever) to prove that you also can use these skills in practice. But still I'm not really sure if this will provide any benefit, because it would require a very special project to show all your skills and I don't think you can easily invent such a project (that sould also be useful).

Others suggested to solve for example the Project Euler questions but still I'm not sure how this will be useful in career-planning. Are you going to mention at your job interview that you solved all this question in the company's favorite programming language?? :D I can't imagine.

The reason why I'm asking is that I have some spare time and I would really like to learn some new programming languages (C++ and/or Python if this matters) and I'm looking for a smart way to do is while concurrently assure that it will be useful in my future career. (there are 3-4 companies id like to try to get a job andIi know all of them are using mainly C++/Pyhton...)