As of now, I do not own a Raspberry Pi, but I really want to buy one. I really want to know what programming languages it supports. What programming lanaguages does it support, and does it support HTML 5 in its browser? I only know that it can run Python scripts and that there's a Minecraft Pi, so it must also support Java - but does it support anything else like C/C++ or C#?
Being a linux computer, it supports basically tens if not hundreds of programming languages, you just have to install the support you need if it's not installed.
Besides Python, Java, C/C++ you may use PHP, bash scripting, AWK, assembly language, LUA, JS scripting, HTML/CSS (is it a programming language?), Clojure, Haskell, Erlang, Forth, Pascal, TeX, SQL, Ruby, Smalltalk and so on... it's by no means a complete list.
And importantly, Mathematica (Wolfram Language). Already installed and free.
The Raspberry Pi has a large suite of programming languages at your disposal. Pre-installed is the GCC compilation software. This allows you to program in languages such as C, C++, C# and (possibly) FORTRAN.
Also installed is the Java Development Kit. This allows you to compile and run Java programs.
The main programming language is Python with both version 2.7 and 3.2 installed already.
For shell scripting, Bash is available.
The Pi also allows for Ruby, Perl and Lisp.
If that isn't enough, you can always download other compilers and interpreters using apt-get or binaries off the web.