I'd guess C++ but I don't know how one could tell that for sure unless it is revealed on their site somewhere.
It's been a while since I played RO, but I'm 99% sure it's written in C++. I believe that the server component is also written in C++, but there are a couple of different implementations of both, including some open source applications.
It is really c++. You can see in the dump of the binary executable file. There are strings with the names of some libraries and system calls, typical of a c++ compiler job.
yea its done in C++, can do alot of good stuff with that language once you get the hang of it. creating an MMO from scratch is extremely hard. if you are thinking of doing so, i suggest making many one player games in C++ so you really get fluent with it, then you can think of tackling an MMO with some friends perhaps.