The Forum is a Jahia App so it is a mix of some definitions/views and templates from the studio.
The Forum reuse pages and topics/posts from the standard Jahia 6.5 installation.
The Studio Templates inside the Forum define page template for the Forum Home/Room/Section pages. Those templates uses some specific Forum components like forumNavigation:
[jnt:forumNavigation] > jnt:content, jmix:bindedComponent, jmix:forumContent
It uses also some custom lists to render topics/posts.
We are creating pages for room/sections to avoid inventing the wheel again. So the Jahia App is really designed from the studio and we add the missing stuff on the flow (navigation,lists,etc.). The usage of pages as start point allows us to reuse a maximum of components from the standard libray of Jahia 6.5 (page from creation for example).
Then we define some content templates for rendering topics, creating new one.
The Forum is a monolingual Jahia App this means that each content is not attached to a language in particular but can be created/read from any language. So people in visiting your site in french will see the same Forum as the one visiting it in english. To create pages that exists in all language just uncheck the Pages created will be internationalized in the Page form creation component.
The forum comes with a whole subset of permissions to allow you to customize what people can do on it :