What language was Diablo written in?

I really love Diablo (the first one, the second ruined the franchise but getting rid of the atmosphere and making it about collecting items as currency) and want to know what language it was written in. Also, I'm currently playing on US East if anyone wants to play with me.

I really wish Blizzard would fix the fucking hacking though. It should take them a single engineer to do it at this point.

The skill and monster systems are now completely data-driven.
Skill balancing is simpler and quicker.
Monster control/populating/creation is simpler.
Although done for our needs, mod-makers should like these changes, too.
A major result is that nearly any skill can be used by any character class.