Hi,
when using "Content" language negotiation, I would expect to be able to change (as far as possible) the content language and interface language independently one form the other, but there are still some issues that prevent that, see the meta-issue #2860901: Doubts about Content language negotiation.
One of the things I noticed is that LanguageNegotiationContentEntity::processOutbound() operates only when these conditions are met:
- URL points to an entity;
- AND it refers to the current request.
The result of this is that on non-entity pages, like for instance the front page, a link to an entity would change the interface language because the query string to change the content language is missing.
Look at the image:
This could be fixed by relaxing the conditions from above in LanguageNegotiationContentEntity::meetsContentEntityRoutesCondition().
A tentative patch is on its way.
Thanks,
Antonio