What language is Synfig written in? Right now I’m studying C++. I looked for the source files but couldn’t find any for windows. 
All the code is C++. There are tree main trunks. ETL: a template library. synfig-core: the command line program (and the libsynfig one) and synfig-studio: the GUI that uses GTKmm libraries.
Please see those wiki page for further information:
Cheers
The source code compiles for Linux, Mac and Windows. Synfig itself is fairly OS agnostic, and uses GTK calls to display dialog boxes on the screen, rather than Direct x or Windows APIs. GTKmm then takes those calls and translates them to Windows calls. The only real ‘Windows’ code is the Nullsoft Windows Installer packager.
The easiest way to see what’s happening is to set up the Windows build environment under Mingw/MSYS and start playing.
synfig.org/Mingw_installation
synfig.org/Windows_build_instructions
Hey thanks guys. I may look around the code and maybe help out in the coding in the future if I can find some free time. Studies take priority. 
Feel free to drop into #synfig on IRC also. You can learn a lot by listening to (or starting) discussions there.
Good luck with the studies.
Chris