Hello community, summer is almost here for me (finish exams in 10 days), and I wonder which programming lang could I learn during summer vacation when I will have a lot of free time.

I already know pretty well C++/C , HTML/CSS/JS 
and also know (not expert) Java,PHP,C#.

Any opinions? Should I learn Java or PHP better or move on to another new lang , like Ruby , Python.
I also want ideas about projects in any of these langs, to practice :)