Should I put my focus into mastering one language or have fun with the languages I want to learn and find which one I want to master?
That usually means that you should be focusing on one or two languages, building enough to have "used them in anger", and then figuring out what to do.
On the other hand, since it takes ten years to become expert, you may not want to wait before starting to learn alternatives. But as a newbie, you don't want to switch to other things too early either. You should have written a couple of non trivial programs (eg. a real application) with a language before you switch to another.
"Mastery", "until I know it all", "find which ones I [like]" all kinda fit into this process, so you end up doing them all at once.
If your java or php or sql or haskell or python suck, the reason your users can tell that they suck, is because your machine code sucks.
The simple awareness of what goes on under the hood will make you better at any language.
Aside from that its helpful to learn several distinctly different paradigms, like python, lisp, c++ and smalltalk.