The language of your OpenGL implementation is completely irrelevant and there is no one answer. Even on a fairly locked down operating system like Windows, the code contained in the library you link to is just a thin wrapper to communicate with the driver. The language the driver is written in is anyone's guess. Probably C and Assembler. Maybe not. Maybe something else.
The driver will communicate with the graphics card (unless it's a pure software OpenGL implementation, which is possible but not a common use case during game development) where the commands will be run by the manufacturer and model specific hardware.

The point you have to concern yourself with is the C interface defined by OpenGL. Any language which can link to C functions can use OpenGL (pretty much every language which could be used in a production environment can do that). Using a thin C library as a binding any such language could also to be used to create an OpenGL implementation.