Continuing the discussion from Plone user manual:
What does the personal preferences language choice do? (Step 15 on Your Personal Profile and Settings – Content Editing for Plone — Plone Training 2024 documentation)
....it would seem from this that it doesn't actually do anything:
If so, maybe we should make it clearer in the field description and in documentation/guides.
...so it's true, this setting is just informational and does nothing else?
Indeed, it seems so.
The language field for a new content item gets its default from the language of the parent/container.
If a user visits the root of a multilingual site, the default language is negotiated based on various factors (see plone.i18n/plone/i18n/negotiate/negotiate.py at master · plone/plone.i18n · GitHub) but the authenticated Plone user's language preference is not one of those. (The preference in browser settings, which is sent in the Accept-Language header, is used here.)
The setting would be more useful if we changed the CMS UI to always show UI text in the user's preferred language instead of in the current content language.
Sounds quite complicated, even without that personal language setting being in the mix... I can imagine a user being puzzled trying to understand why a certain language is being shown to them, and how to change/fix that. There would need to be some explanation that could be shown.