main ← fix-sidebar-source-locale
merged 03:49PM - 03 Aug 26 UTC
Previously, the custom sidebar section editor and the server assumed a section's… base title and link names were written in the site's current *default* locale, so changing the default locale scrambled which language each stored value mapped to and offered the wrong set of translation targets ([meta](https://meta.discourse.org/t/408327)).
This change keys the editor, the same-locale de-duplication and the collision cleanup off each record's own source locale — now surfaced as an editable "Section language" — and reorganises the translation UI around languages rather than fields.
### Notable behaviour changes
- Links keep their own source language, so saving a section no longer relabels a link authored in a different one.
- A localization colliding with its record's source is now destroyed instead of being left behind to shadow the base string. The collision is matched **exactly**, so a regional variant like `en_GB` under an `en` source is preserved.
- Localization permissions are evaluated against the visibility being *submitted*, so making a section public and translating it in one save no longer 403s and loses the edit.
- `create` now enforces localization permissions, which it previously skipped entirely — an admin could write localizations onto a private section. A non-admin submitting localizations on create now gets a `403` instead of a silent drop, matching `update`.
- A submitted locale is validated at the request boundary: an unsupported or over-long value returns `400` rather than an unhandled `500`. A value already stored on the record is still accepted, so AI-detected locales outside the supported list stay editable.
### UI
<img width="821" height="646" alt="2026-07-29 @ 14 56 10" src="https://github.com/user-attachments/assets/19dad480-9f77-4f5b-b1a6-ed29689839a8" />
<img width="820" height="666" alt="2026-07-29 @ 14 56 16" src="https://github.com/user-attachments/assets/a9377282-d4b2-43af-91a6-700e10c50ce6" />
Translations moved from inline per-field rows to a single "Manage translations" entry point opening a language-major panel — one group per language holding the section title and every link name. The old layout rendered `1 + links × languages` rows with an add button per field, which stopped being usable at three links and two languages.
A blank field means "not translated yet" rather than invalid, and clearing a saved translation now asks for confirmation before removing it.