Add a new country to countries list

wc-add-new-country.php

<?php
add_filter( 'woocommerce_countries',  'gnwooc2_ajouter_pays' );
function gnwooc2_ajouter_pays( $countries ) {
  $new_countries = array(
	'NIRE'  => __( 'Irlande du NORD', 'woocommerce' ),
	);

	return array_merge( $countries, $new_countries );
}

add_filter( 'woocommerce_continents', 'gnwooc2_ajouter_pays_continents' );
function gnwooc2_ajouter_pays_continents( $continents ) {
	$continents['EU']['countries'][] = 'NIRE';
	return $continents;
}