register_nav_menus()

function register_nav_menus( $locations = array() ) {
	global $_gc_registered_nav_menus;

	add_theme_support( 'menus' );

	foreach ( $locations as $key => $value ) {
		if ( is_int( $key ) ) {
			_doing_it_wrong( __FUNCTION__, __( 'Nav menu locations must be strings.' ), '5.3.0' );
			break;
		}
	}

	$_gc_registered_nav_menus = array_merge( (array) $_gc_registered_nav_menus, $locations );
}

function cebbi_update_menu_location() {

	// Get assigned menus from theme mods
	$nav_menu_locations = get_theme_mod('nav_menu_locations');

	// Check if old-slug was previously assigned
	if (isset($nav_menu_locations['old-slug'])) {

		// Verify that new location does not yet exist or is empty to avoid overwriting manual changes
		if (!isset($nav_menu_locations['new-slug']) || $nav_menu_locations['new-slug'] === 0) { 

			// Copy assigned menu index to new location
			$nav_menu_locations['new-slug'] = $nav_menu_locations['old-slug'];

			// Optional: delete the menu assignment to the old location
			unset($nav_menu_locations['old-slug']);

			// Update theme mod
			set_theme_mod('nav_menu_locations', $nav_menu_locations);
		}
	}
}
add_action('after_setup_theme', 'cebbi_update_menu_location');

$tax = 'country-category';

$terms = get_terms( $tax, [
'hide_empty' => false,
]);

$args = array(
'primary' => __( 'Primary Menu', 'khoipro' ),
'secondary' => __( 'Secondary Menu', 'khoipro' )
);

// Loop through all terms to add term id as menu id and term name as menu name.
foreach( $terms as $term) {
$args = array_merge($args, array(
'primary_'.$term->slug => 'Country Menu ('.$term->name.')'
));
}

register_nav_menus( $args );