fix: add fallbackLocales to show translations even if there is no connection to the server

[SGrueber]

PR Type

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no API changes)
[ ] Build-related changes
[ ] CI-related changes
[ ] Documentation content changes
[ ] Application / infrastructure changes
[ ] Other:

What Is the Current Behavior?

Precondition: the pwa cannot connect to the ICM server, e.g. because of a wrong base URL

• without SSR (multichannel configuration) - if the user requests a page in German (route parameter lang=de_DE) the error page will be shown in English
• with multichannel config: The translations of the json files are not returned all texts are missing in the page (missing translation is shown)

Issue Number: Closes #

What Is the New Behavior?

The error page is shown in the requested locale if the server doesn't respond

Does this PR Introduce a Breaking Change?

[ ] Yes
[x] No

Other Information

AB#79145
AB#78921