What's the origin and what's the nationality?
No nationality. Esperanto is a constructed language, it was planned to be used worldwide. However that idea hasn't been realized yet.
The origin is an idea of a neutral, easy to learn, international language which could be a second language for everyone so that people can easily understand each other. The idea was that a universally understood language would go some way towards preventing war. It is not there yet, but by some estimates there are 2 million speakers already, so even if it is not a universally spoken language, there are probably people speaking it wherever you want to go.