In this documentation you will learn
Admin panel > Left menu > SETTINGS > Country
All countries that is used for custmer order,shipping,etc. is listed under this admin section.
Screenshot 1 : Country List.
Below is a screeshot that is showing an example of country edit form (code,name, full name as name2, iso3, Number, sorting,continent).
Screenshot 2 : Country editing form.
Considering country language
In default Cart21, All country is registered in English but if you decided to publish the website in another language, after activating the language country edit form will be open for that language that means you have to edit each country for the custom language.
How to change order of country that is listed in front side
Screenshot : Country list on cart static page.