I'm not sure I believe your assertion that they're "a totally different language." A simple hello world app in C using the standard runtime library might look like:
#include <stdio.h>
int main()
{
puts( "Hello World!" );
}
while using the windows API it looks like:
#include <windows.h>
int main()
{
MessageBoxA( NULL, "Hello World!", "Hello", MB_OK );
}
The only difference there is the function you use to do the output.
Write a standard C program that needs to dispatch a set of nested commands and you'll see that Windows programming using the Windows API is very much C programming. I'd suggest reading "Programming Windows" by Charles Petzold as a good first start on becoming a proficient GUI programmer on Windows. You want the 5th edition which came out about 2000. It's an old book and some of the programming techniques grate a bit but it's a very good introductory book.
Cheers,
Ash