Translation does not work across domains/websites if the translated content of a second language is the default language of another domain/website
website  domain.de
default language: German (Base: "/"; de_DE.utf8; de-DE)
additional language: English (Base: "/en/; en_GB.utf8; en-GB; Fallback: "Strict: show only translated content, based on overlays)
website  domain.ch
default language: Switzerland (Base: "/"; de_DE.UTF-8; de-DE) - I noticed that this might be wrong in terms of SEO so I wanted to switch it to "de-CH" and "de_CH.UTF-8"
additional language: French (Base: "/fr/; fr_CH.utf8; fr-FR)
website  domain.co.nz
default language: English (Base: "/"; en_NZ.utf8; en-GB)
I want to use translated news records, event records from website  on website  (cross-domain, in English) but that's not possible.
To make it work I have to create a "fake" English default language on website  which I have to disable so it will look like this:
default language (disabled): English (Base: "/"; en_NZ.utf8; en-GB)
additional language: English (Base: "/"; en_NZ.utf8; en-GB)
Now I can use the translated news records from website  on website .
The same problem appears on website  and  with German and Switzerland, only there it's not that obvious because Switzerland is also a German speaking country, so using the default language for news records works (besides I have to change ß into ss) manually.
I think the correct way would be to translate the German news to the Switzerland localization and then use the translated news on website  but that's not possible because I would need to add German as the default language and disable it as well.
I also noticed that German is not available as language record on the root site [id=0].
Wouldn't it be better to have all available languages for a TYPO3 instance on the root site [id=0]? The you can choose the desired languages for a website in the site configuration and maybe translations cross-domain would work that way? I would imagine that having German as an additional language on another website and then I want to use the German news records wouldn't work too.
It should be possible to use a language as the default and an additional language on different websites/domains and use translated records.
Can anyone reproduce and confirm the issue? I don't know if the issue still exists on TYPO3 10.