Is it possible to make the game online, as they did the same SAMP, for example?

Question

Programming

Hello.
Some time ago I came across the game Star Wars: Knights Of The Old Republic . I liked the toy, and I thought: "Oh, if it were online ...".
Actually, can multiplayer be attached to each game (if they give you, of course)?
I'm not saying that the game is popular and in general it will be profitable, but it would be cool, at least for a narrow circle of people.
What are these things written on? C++/Java? How difficult is it from a technical point of view, what skills are needed?
Z.s. SAMP-GTA: San Andreas MultiPlayer