On the sidebar, under Notifications, you will be able to toggle your subscription to the thread.
You can also now manage notification settings at the individual issue or pull request level. This lets you manually subscribe to any issue without commenting, or unsubscribe from issues no longer relevant to your interests:
See the blog post, "Mention @somebody. They're notified." for details.
It is currently not possible to easily do internationalisation for GitHub wiki pages and/or GitHub Pages, but you can if you do quite a bit of changes.
Lets say for example, the main working language in your repository is English. You can create pages in the wiki with the content in English (so the page called "Installation" will provide details on installing the software).
If you want to make your repository's wiki offer content in another language, I would suggest that you use prefixes to differentiate out the different languages. GitHub does not allow subpages in the wiki, so you can use something like "De:Installation" ("De" is the language code for German) to serve German content for the page on "Installation".
Of course, the wiki will always have a page called "Home" to serve as the entrance page. Use it to link to various other language homepages (e.g. "De:Home") and from there, link to the various other pages that starts with "De:".
Finally, send an announcement to everyone who collaborate with your project regarding this change so that they know how to create new pages in a language different from English.
For GitHub Pages, its purely using HTML to generate the website. Make use of that fact to create a website that can serve content in various languages. Upload your files to the "gh-pages" branch of your repository.
Hope this helps!
Best Answer
You might try Figurepool to create a diagram, generate a Markdown code snippet that it provides and just copy paste the snippet into the Github wiki. Check out this blog post: http://figurepool.com/blog/Embedding_images_and_diagrams_in_github_wiki_pages_and_issue_tracker.html.