The following will show you how to add country codes to your site in order to allow users to choose their country when signing up for an account or to comment on the site.
You will need content editor, admin or super admin access to do this. Once you log in you will select the publishing tab
You will then scroll down toward the bottom of the page and on the left you will see "Country Editor", select it
You will be brought to a page that shows the existing countries. Here you can edit an existing one or create a new one by selecting the "New" button.
Add the desired country and it's two-letter code using Country Code as a guide. When you are finished, select "Save & Done".