Steps to reproduce

1.  Change superuser preferences to use German as preferred language.
2.  Log out and login again
3. Make pages app (Ui-5) available in the app launcher (or contacts-v8 if you prefer)
4. Access travel with pages-app (new UI-6) (link)
5. Access travel with pages app (old UI-5) (link)

Expected results

Both pages should display the content in the same language, the default/fallback content language for the site.

Actual results

UI-5: user language, if the user language is a valid i18n value
UI-6: default content language

Workaround

N/A

Development notes

Related to MGNLUI-6501
This also can be tested in content apps such as contacts / contacts-v8 or assets/dam-app, but you need to add internationalisation to these apps.