materio-d8/web/modules/custom/materio_sapi/src/CountryNameNodeComputed.php

<?php

namespace Drupal\materio_sapi;

use Drupal\Core\Field\FieldItemList;
use Drupal\Core\TypedData\ComputedItemListTrait;
// use Drupal\Core\StringTranslation\TranslatableMarkup;

class CountryNameNodeComputed extends FieldItemList {
  use ComputedItemListTrait;

  protected function computeValue() {
    $node = $this->getEntity();
    $node_lang_code = $node->language()->getId();
    // $distrib = $node->get('field_distributor')->referencedEntities();
    // $manuf = $node->get('field_manufacturer')->referencedEntities();
    $companies = array_merge($node->get('field_distributor')->referencedEntities(), $node->get('field_manufacturer')->referencedEntities());
    $country_codes = [];
    foreach ($companies as $term) {
      $address = $term->get('field_public_address')->first();
      if ($address) {
        $country_code = $address->getCountryCode();
        if (!in_array($country_code, $country_codes)){
          $country_codes[] = $country_code;
        }
      }
    }
    if (count($country_codes)) {
      $full_country_list = \Drupal::service('country_manager')->getList();
      foreach ($country_codes as $i => $country_code) {
        /** Drupal\Core\StringTranslation\TranslatableMarkup **/            
        $country_name = $full_country_list[$country_code];
        // $country_name->options['langcode'] = $this->langcode;
        // $lang = \Drupal::languageManager()->getCurrentLanguage()->getId();
        $untranslated = $country_name->getUntranslatedString();
        // $translated = $country_name->render(['langcode' => $node_lang_code]);
        $translated = t($untranslated, [], ['langcode'=>$node_lang_code]);
        // $this->list[$i] = $this->createItem($i, "lang: $lang, node:$node_lang_code, $untranslated, $translated");  
        $this->list[$i] = $this->createItem($i, $translated);  
      }
    }
  }
}