Over the past 2 years i've been learning languages like Java, C, C++, Python, SQL, ..
I also learned some less significant things such as LaTeX, VBA, scripting in unix shell, how to use CGI scripts and HTML and CSS.
I have learned all of these quite thourougly, not just some Hello World!-applications...
But how does one maintain so 'many' different languages and all of their aspects?
If someone told me to set up a program in Python now, i would have no clue on how to start, i would first have to go through my study books again.
Don't worry about it. You may be thinking "use it or lose it" - and there's an element of that to the experience, but it's more a matter of, if you're not using it, it's probably because you don't need it right now. When the time come and you do need - let's say python - again, sure, it will take some time to come back up to speed, but it will nevertheless be a great deal less effort than if you had never gotten your head around it in the first place.
Don't try to keep your head cluttered with everything at once; you probably can't. Learn what you want, hang on to the important bits (you will probably do this without trying), and let the messy details slip away until you need them. If you have to look them back up at that point, that's OK.