Each download will include a zip file that you need to uncompress in the root of your installation. The included files are all the resources available in the project, at this time:
And for each of the main templates
All downloaded languages will be available in the switcher in the top bar of your installation. You can switch between any of them by opening the dropdown and selecting you new language for the current session.
To have a language as default for all users and sessions open your configuration file at /includes/sys.config.php with a text editor of your choice.
There, find the line that reads something like this:
And change the value to the name of the file of your language minus the file extension.
For example, if you want to use the French language, change it to
If your language is localized, like in the case of Portuguese (which has the Brazil and Portugal variations), be sure to include the full name. For example, for Portuguese (Brazil), use