ProfileFieldTranslation.php

<?php

namespace Drupal\config_translation\Plugin\migrate\source\d6;

use Drupal\user\Plugin\migrate\source\ProfileField;

/**
 * Gets i18n strings profile field source from database.
 *
 * @MigrateSource(
 *   id = "d6_profile_field_translation",
 *   source_module = "i18nprofile"
 * )
 */
class ProfileFieldTranslation extends ProfileField {
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        $query = parent::query();
        $query->fields('i18n', [
            'property',
        ])
            ->fields('lt', [
            'lid',
            'translation',
            'language',
        ]);
        $query->leftJoin('i18n_strings', 'i18n', 'i18n.objectid = pf.name');
        $query->innerJoin('locales_target', 'lt', 'lt.lid = i18n.lid');
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        $fields = [
            'lid' => $this->t('Locales target language ID.'),
            'language' => $this->t('Language for this field.'),
            'translation' => $this->t('Translation of either the title or explanation.'),
        ];
        return parent::fields() + $fields;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        $ids['language']['type'] = 'string';
        $ids['lid']['type'] = 'integer';
        $ids['lid']['alias'] = 'lt';
        return parent::getIds() + $ids;
    }

}