Hi,

I am a current GSoC student on GCC, so I'll let some of your questions to
more veteran contributors. However, feel free to also reach out to me if
you got any questions as to where to start, as I consider myself just out
of this phase.

Programming Languages: Which programming languages are commonly used in
   GCC projects? Are there any specific languages that you recommend
beginners
   to focus on initially?

GCC is written in a customized mix of C++ and C. Some C++ standard
constructs have been handmade, such as vectors. However, if you are
familiar with C++, I believe you'll adapt quickly to those. If you consider
contributing to some language front-end, or to some specific back-end, then
knowledge on that front will always be useful. However, from my short
experience, I can already tell you that GCC is in itself a great teacher,
as long as you have the basics, or put the extra effort to get them, you'll
step up your game quickly.

Tools: What are the essential tools utilized in GCC projects? It would
   be helpful to know which tools are commonly used for tasks such as
version
   control, project management, documentation, and testing.

Git is the one tool you have to get used for GCC, as for testing it is a
bit old-fashioned with a TCL based testsuite (see Dejagnu). I'd encourage
you to try install GCC from the sources, and poke around them in your
favorite editor. It might be a bit rough at first, but that's also how
you'll progress quickly.
Obviously, if you consider contributing to the development of GCC, you will
need to be debug some things. I think GDB is the most used debugger here.

 Learning Resources: Could you please recommend any online resources,
   tutorials, or documentation that can assist beginners in understanding
GCC
   projects and the associated technologies?

I would recommend https://gcc.gnu.org/contribute.html obviously, but also
https://gcc-newbies-guide.readthedocs.io/en/latest/index.html, that will
soon get extra content. If you decide to take a look at the sources, see
the documentation https://gcc.gnu.org/onlinedocs/gccint/index.html.
I am also writing a blog to keep track of my GSoC project, once I have a
proper open source license set up I will send you the link (in a few hours
if I'm not lazy).

Good luck and feel free to reach out,
Benjamin.