I don't really see how knowing what this particular game was written in can help in anything, but here goes:
After investigating the windows package I'd make a strong educated guess that it's C++ (and of course parts might be written and linked as pure C, since that is no problem technically).
Why? Without poking too too deep and without specialized tools:
1. There are a lot of PE32 dlls, some of which are widely used C libs.
2. Executable too is PE32.
3. There is this string in the executable, hinting at the compiler*: "GCC: (GNU) 4.9.0 20130525 (experimental)".
4. There are strings in there (exe) that look like C names and mangled C++ names*.
5. There are these paths in there:
C:\repos\New Engine\SOURCE\UTIL\TmxParser\tinyxml\tinyxmlparser.cpp
C:\repos\New Engine\SOURCE\UTIL\TmxParser\tinyxml\tinyxml.h
C:\repos\New Engine\SOURCE\UTIL\TmxParser\tinyxml\tinyxml.cpp
hinting that tinyxml is used, but I can't guess why they are there, I thought it might be from __FILE__ macros used in error messages, but there don't seem to be any (except for one on android) in tinyxml.h and tinyxml.cpp on github.
... (the list goes on, but it's just more of the same - symbol names, strings, guesses ect.)
Of course this is all educated guessing AND it's always possible this was written in a language that is source compiled to C/C++ in the end (Haxe can do this, among numerous other backends), but chances are slim.
*although if you want to troll someone who is doing what I'm doing right now, you can include strings with names of all common toolkits function names and programming language toolchains in your exectuable to throw the "investigators" like me off, that'd be fun, and I don't think this is going on in here.