The Github Wiki is managed by Git, so all you have to do is "git clone" the Wiki's Git repository. You can back up the entire page.
git clone https://github.com/yuki-kimoto/perlzemiubuntu.wiki.git
Edit and push locally
The Github Wiki is just a Git repository, so you can edit it locally and "git push" it.
This is useful when you have content that you want to modify as a whole.