FieldOptionTranslation.php

<?php

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

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

/**
 * Determines the allowed values translation for select lists.
 *
 * @MigrateProcessPlugin(
 *   id = "d6_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) {
        [
            $field_type,
            $global_settings,
        ] = $value;
        $allowed_values = '';
        $i = 0;
        if (isset($global_settings['allowed_values'])) {
            $list = explode("\n", $global_settings['allowed_values']);
            $list = array_map('trim', $list);
            $list = array_filter($list, 'strlen');
            switch ($field_type) {
                case 'list_string':
                case 'list_integer':
                case 'list_float':
                    // Remove the prefix used in the i18n_strings table for field options
                    // to get the option value.
                    $option = preg_replace('/^option_/', '', $row->getSourceProperty('property'));
                    $i = 0;
                    foreach ($list as $allowed_value) {
                        // Get the key for this allowed value which may be a key|label pair
                        // or just key.
                        $value = explode("|", $allowed_value);
                        if (isset($value[0]) && $value[0] == $option) {
                            $allowed_values = [
                                'label' => $row->getSourceProperty('translation'),
                            ];
                            break;
                        }
                        $i++;
                    }
                    break;
                default:
            }
        }
        return [
            "settings.allowed_values.{$i}",
            $allowed_values,
        ];
    }

}