Adding language based URL structure

If you’re talking about pages, you can create a parent page with the country code as it’s URL and set all the other pages as children of it. You could even make that page the homepage for that language.

If you mean posts, you could create a custom taxonomy and follow these instructions to add it to your permalink structure.

There are also lots of multilingual plugins that might help you, such as Polylang and WP Multilang (this one looks like it might support the language code in the URL).