You don't need to know any coding language.
Allods itself uses java but all the files that you can edit are .xdb and they have a very easy structure. Just read them and you will understand how it works.
That guy that disappears every few weeks for a few months
You don't need to know much coding to host any server. You should have a basic understanding to make your life easier, yes. There are plenty of guides around here which will help you in every step of the way to get your server up and running.
To develop and create new content is a different story, then it depends then on what game and which core you are using. I would maybe start out with a core that uses Eluna, that way you can write scripts in LUA which is a well documented and easy to learn language. Other than that, if you want to get serious then C++ is basically the mother of all.