I have been there 6 years ago for one week as an individual volunteer. Officially the maximum time for an individual volunteer is one week but if things goes well you can extend it. There I've been on different workshop that you may not always be able to choose as it depends on demands from others workers. On the first day, I've been building a roof for a future workshop with wood tile, then I have helped some mason building the castles walls for 2 days. The last 3 days I have spent them doing stone-cutting for the castle. Most of people that work there are passionate about their work so it is communicative. What I really enjoyed there is that sometimes I really felt like I was living in the middle age during a few minutes.

For non-french speaking people I would say just go there I'm sure you'll find people speaking english that will help you, it should not be a problem. Here is the page about volunteering: http://www.guedelon.fr/fr/comment-participer-aux-travaux_40....

Just use google translation for it if you cannot read french