Create a shortcode for a handmade plugin in Wordpress - wordpress

Question

I'm working on WordPress actually and created a plugin from scratch, fully working on admin page.
The plugin allow you to add country and languages related (USA->English|Sapnish for example)
I am using Class and constructor for the plugin's functions
Now I would like to created a select with country and depending on country another select with languages. I know how to create this in js/html but I can't find a way to get the data from the plugin.
I tried :
Create a function (in the plugin) who used plugin's other functions (see below)
public function getCountry()
{
global $wpdb;
$table_name = $wpdb->prefix . "country_wmu";
$results = $wpdb->get_results('SELECT * FROM ' . $table_name);
if ($wpdb->last_error !== '') {
echo '<p class="info-wmu error">Une erreur est survenue</p>';
} else {
return $results;
}
}
public function getLang($id)
{
global $wpdb;
$table_name = $wpdb->prefix . "lang_wmu";
$results = $wpdb->get_results('SELECT * FROM ' . $table_name . ' WHERE _id_country = ' . $id);
if ($wpdb->last_error !== '') {
echo '<p class="info-wmu error">Une erreur est survenue</p>';
} else {
return $results;
}
}
public function wmu_get_data($atts, $content=null)
{
$country = $this->getCountry();
foreach ($country as $key => $value) {
$country_id = $value->id;
$lang = $this->getLang($country_id);
foreach ($lang as $key2 => $value2) {
$country[$key]->lang = array(
'name' => $value2->name,
'url' => $value2->url
);
}
}
return $country;
}
and then add shortcode
add_shortcode('wmu_data', 'wmu_get_data');
and displaying the shortcode in the page, but shortcode displays as plain text
[wmu_data]
So I tried to do a function in my functions.php to do a do_shortcode, then add a shortcode to this function.
function test()
{
$country = do_shortcode('[wmu_data]');
echo '<pre>';
print_r($country);
echo '</pre>';
}
add_shortcode('test','test');
But nothing happens, blank page...
I really don't have many more ideas to do it...
EDIT:
I found out with the error code, Have to use
add_shortcode('wmu_data', array('WB_MultiLang_URL','wmu_data'));
to call it outside the function
thanks Larjos for pointing out the problem at his root :)