Multilingual Hub Menu is not translating

Hi Sabine_DB 

I have never figured out why most times the changes in Account settings for display language are synchronized to Profile language settings, and sometimes not.  If you tinker too much with both, at some point it stops synchronizing until the next day.  The account setting for preferred display language is single-valued, while the profile setting is a ranked list.  Changes sync from the account to the profile but not the other way around.  From the profile, it syncs to every site, slowly but reliably.  Changes made at the site level do not sync upwards to the profile.

For Hub navigation there are several levels of caching.  The one that is covered by the API is here
https://learn.microsoft.com/en-us/sharepoint/dev/features/hub-site/rest-hubsitedata-method
Note the forceRefresh parameter.  Yes, it's a server parameter change in a read request.  But that is only part of the story.  This API is for the server cache, not the browser cache.  The browser cache is not covered by API, and its mechanism changes now and then. Our product development team spends its time tracking those changes and making the cache update.