Translatable image field gets replaced when adding content
By default only the image alt and title are translatable and the file itself isn't. By the default the file is always the same in all languages. You can simply make the file to be translatable as well under https://example.com/admin/config/regional/content-language.



Note: After you've done this, all your existing translations will need to have the file re-uploaded (or a new file uploaded), as the default only gets added once when translating content through the UI.



Taken the above Hero image field this can be done manually be editing field.field.node.page.field_hero_image.yml (which translates to field.field.ENTITY_TYPE.BUNDLE.FIELD_NAME.yml):

Before file checked:

third_party_settings:
  content_translation:
    translation_sync:
      alt: alt
      title: title
      file: '0'


After file checked (alt and title are mandatory if file is checked, that's why they have '0' now):

third_party_settings:
  content_translation:
    translation_sync:
      file: file
      alt: '0'
      title: '0'