Did you try to include wp-blog-header.php
instead?
Your external file:
define( 'WP_USE_THEMES', false );
require('wp-blog-header.php');
do_shortcode('[CBC country="us" show="n"]');
I just tried the following and it worked:
External file:
define( 'WP_USE_THEMES', false );
require('wp-blog-header.php');
do_shortcode('[displayshortcode]');
functions.php file:
function shortcode_function() {
echo 'shortcode';
}
add_shortcode('displayshortcode', 'shortcode_function');