ImportService assumed entity langcode field is called 'langcode'

Problem/Motivation

> InvalidArgumentException: Field langcode is unknown. in Drupal\Core\Entity\ContentEntityBase->getTranslatedField() (line 616 of /app/web/core/lib/Drupal/Core/Entity/ContentEntityBase.php).

with an entity such as a redirect, because this hardcodes the field name:

        $existing_entity->set('langcode', $data_langcode);

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes