A country is a nation with its own government, occupying a particular territory or piece of land. For example, China, France, Iraq and Japan are all countries.
"Country" is a political term, not geographical. In theory, all countries are sovereign, meaning that they are independent and decide their own laws (though they may sometimes surrender or modify certain rights by treaty).
The noun for a country's language usually comes from the adjective for that country, for example:
In English, all words (nouns and adjectives) relating to countries or nationalities begin with a capital letter, for example: