FieldOptionTranslation.php

<?php

namespace Drupal\field\Plugin\migrate\process\d7;

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

/**
 * Determines the allowed values translation for select lists.
 *
 * @MigrateProcessPlugin(
 *   id = "d7_field_option_translation",
 *   handle_multiples = TRUE
 * )
 */
class FieldOptionTranslation extends ProcessPluginBase {
    
    /**
     * {@inheritdoc}
     *
     * Get the field default/mapped settings.
     */
    public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
        [
            $type,
            $data,
        ] = $value;
        $data = unserialize($data);
        $new_allowed_values = '';
        $translation_key = $row->getSourceProperty('property');
        if (isset($data['settings']['allowed_values'])) {
            $allowed_values = $data['settings']['allowed_values'];
            switch ($type) {
                case 'list_string':
                case 'list_integer':
                case 'list_float':
                case 'list_text':
                    if (isset($allowed_values[$translation_key])) {
                        $new_allowed_values = [
                            'label' => $row->getSourceProperty('translation'),
                        ];
                        $translation_key = array_search($translation_key, array_keys($allowed_values));
                        break;
                    }
                    break;
                default:
                    $new_allowed_values = $allowed_values;
            }
        }
        return [
            "settings.allowed_values.{$translation_key}",
            $new_allowed_values,
        ];
    }

}