Polylang multilingual site. Ninja forms subscribes user to two different lists

I’m building a multilingual site using Polylang.

I would like to allow my users to subscribe to a different MailChimp list according to the language the chose to see my website in when they submit a form made with ninja forms. Unfortunately, when I test it, the user gets subscribed to both lists.

I added in my function.php the following code:

add_filter( 'mc4wp_lists', 'myMc4wpI18n');
add_filter( 'mc4wp_integration_lists', 'myMc4wpI18n');
add_filter( 'mc4wp_integration_' . $slug . '_lists', 'myMc4wpI18n');

function myMc4wpI18n ( $lists ) {

   $map = array(
      'en' => 'XXXXXXXXXXX',
      'it' => 'XXXXXXXXXXX'
   );
   $site_language = pll_current_language();
   if( isset( $map[ $site_language ] ) ) {
      $list_for_language = $map[ $site_language ];
      return array( $list_for_language );
   }
   // return default lists
   return $lists;
}

but it doesn’t work.

Hacking the code, I found this $ninja_forms_processing global variable, but I don’t know how I could apply the same filter there.

Any hint?

https://wordpress.org/plugins/mailchimp-for-wp/