ProfileFieldOptionTranslation.php

<?php

namespace Drupal\user\Plugin\migrate\process\d6;

use Drupal\migrate\MigrateExecutableInterface;
use Drupal\migrate\ProcessPluginBase;
use Drupal\migrate\Row;

/**
 * Determines the settings property and translation.
 *
 * @MigrateProcessPlugin(
 *   id = "d6_profile_field_option_translation",
 *   handle_multiples = TRUE
 * )
 */
class ProfileFieldOptionTranslation extends ProcessPluginBase {
    
    /**
     * {@inheritdoc}
     */
    public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
        [
            $field_type,
            $translation,
        ] = $value;
        $new_value = NULL;
        if (isset($translation)) {
            $allowed_values = [];
            $list = explode("\n", $translation);
            $list = array_map('trim', $list);
            $list = array_filter($list, 'strlen');
            if ($field_type === 'list_string') {
                foreach ($list as $value) {
                    $allowed_values[] = [
                        'label' => $value,
                    ];
                }
            }
            $new_value = [
                'settings.allowed_values',
                $allowed_values,
            ];
        }
        return $new_value;
    }

}