Updated Drupal to 8.6. This goes with the following updates because it's possible...

[yaffs-website] / web / core / modules / config_translation / migrations / d7_user_settings_translation.yml

id: d7_user_settings_translation
label: User settings configuration translation
migration_tags:
  - Drupal 7
  - Configuration
  - Multilingual
source:
  plugin: d7_variable_translation
  variables:
    - anonymous
process:
  langcode: language
  anonymous: anonymous
destination:
  plugin: config
  config_name: user.settings
  translations: true