Elsewhere on the internet I've heard people say that if you mention it at all, you should put it in hobbies or else you risk getting dismissed and gossiped about to a company's peers, limiting your job opportunities.
We discussed that question here:
I said that if you put Esperanto on your resume, the response at an interview (if you get one) will certainly be "what the heck is that?".
A few people replied that they got their current jobs thanks to having Esperanto on their resume.
For my part, I have it listed at the top of my foreign languages. People have asked about it, or skipped over it. People are always very interested - at least to my face, I suppose.
My thought is that it doesn't belong under hobbies. If you don't speak it well enough to call it a language, it probably doesn't belong on the resume at all. I think it helps if you have more than one language.
Every single time I was asked about it in the interview, and it was always viewed positively, with interest, not something to be frowned upon.
And I absolutely disagree with hiding it. I could. I have two native languages. I could just say I speak Hungarian. No, never, I am too proud to belong to the Esperanto community.
I was very hesitant to put Esperanto in my resume myself because of all the misconceptions people have about it (which are neatly listed here: What are the most common misconceptions about Esperanto?). I decided to do so in the end, after a non-esperanto-speaker told me I should absolutely write it. She said it is a great example of determination and deligence, just like learning any other language.
I have added it to my resume solely because my research advisor at university added "Marathon Runner" to hers for a chemistry teaching position. The only reason I know this is because another professor was on the search committee and he commented on that fact. He remembered that running was on her resume and, while it didn't help or hinder her application, it was something that stood out.
I am of the notion that standing out is good (as long as it's something good or neutral that is making you stand out).
If you only speak English and Esperanto, then I would put it in hobbies, otherwise, I would put it among the other languages that you speak.