Dealing with intern supervisor who underestimates my abilities
I don't say this lightly, but given everything you've said: I think you should probably quit the internship, or at least present the prospect of that to your supervisor.

Some key points:

1) You say it's a "voluntary internship".  Well, all academic internships are voluntary (I hope!), so I think what you mean is that you are a volunteer, i.e., unpaid.  [Added: I just looked this up, and apparently this phrase is quite common in parts of the anglophone world outside of North America.  Sorry.]

2) You wrote


  I was hoping that I was going to work on something productive, like a research project.


That is a very reasonable expectation for a volunteer internship.  However, the parameters of the job seem to be very different:


  I'm a trainee in the lab where programming lessons are held with lots of computers available for the students.


But that doesn't sound research-related at all: it sounds like you're in a teaching lab, not a research lab.  If you were actually doing the training, you'd be some kind of TA...without pay.  Unfortunately:


  On the contrary, my supervisor...constantly assigns chores to me (cleaning, being his personal mailman on the university etc).


Having to clean up a laboratory space after using it is very reasonable.  In my branch of the academic world at least (North America), cleaning up after other people is a paid job, not part of an internship.  Similarly, mail delivery is the sort of thing for which someone is usually paid an hourly wage.  If you are doing some of this and some of something else, it might be okay if the something else were especially attractive and rewarding.  But given that you're not, it sounds to me that you're simply being exploited.  Certainly I would feel that way if I were you.


  Yet, he only has one paper, published 20 years ago.


Yikes.  So the professor is probably not even research-active, or at least not to the level necessary for it to be plausible that he is the head of some kind of research team.  He is not a good choice to supervise your research.  In view of everything else you've said, I'm afraid that it seems likely that the business about your having a "proper foundation" -- especially in the context of his willful ignorance of the skills that you already have -- is just an excuse.  

I would go to this professor and say that there's been a misunderstanding.  You thought you were getting involved in a research internship, and as it hasn't panned out that way, you'd like to give notice.  If he wants to change your mind, have him mention not just the prospect of future research "when you're ready", but actually nail down research that you can get started on right away.  

It would also be good to speak to at least one of the other faculty members you've mentioned.  I don't know where in the world you're writing from, so it's possible that your local academic culture is very different from mine.  But unless you find out that it would be a big bridge-burning mistake to quit your internship, I think you should be angling for that outcome.