Depends on what you want to do.
There are old bots sources, old clients sources, tradebots, proxies....
C#/java/euphoria (damn) but you can use whatever the f* you want.
Getting info on yourself and servers starts by making GET/POST requests to https://realmofthemadgodhrd.appspo*****m/{something}?
->download Fiddler, make it so it read HTTPS STUFF and launch rotmg