Jekyll does not come with any internationalization tools. You will need to install a plugin.
The most popular, currently-maintained plugin is the Jekyll Multiple Languages Plugin.
It is an open source program with the Mozilla Public License.
Use with GitHub Pages
These plugins are not compatible with the GitHub Pages implementation of Jekyll.
Installing
In your project directory, run this command:
git submodule add git://github.com/screeninteraction/jekyll-multiple-languages-plugin.git _plugins/multiple-languages