Wrong display in case of more than one titles / subtitles in various languages

[pronguen]

Bug description

• The displayed title is not always the first of the array.
• The title in another language is not displayed.

Current behavior

A document title is title[], where each entry has mainTitle[] and
subtitle[], each item being {value, language}.

Both UIs display a single title, filtered by the UI language:

• Public UI: title_format (sonar/modules/documents/views.py:105) takes
  title[0] and returns the mainTitle/subtitle value matching the UI
  language, falling back to the first item.
• Pro/admin UI (sonar-ui): document/detail/detail.component.html renders
  title[0].mainTitle | languageValue and title[0].subtitle | languageValue
  (same single-language behavior); the brief view
  (document.component.html) does the same.

So titles in other languages are never shown, and the chosen value depends on
the UI language rather than the array order.

Scope

Fix the display only — keep the current data structure. (The deeper
structure simplification, moving language to the first level, is tracked
separately and is out of scope here.)

Expected behavior

Per the mockup (mockup.pdf):

• Primary title: the first entry of title[0].mainTitle (array order,
  independent of the UI language). Append, if present, the title[0].subtitle
  whose language matches that main title's language.
• Other-language title(s): below the primary title, display the remaining
  mainTitle entries (other languages), each with its matching-language
  subtitle if present.

This applies to both UIs:

• Public UI: update title_format.
• Pro/admin UI (sonar-ui): update the detail view title rendering (and the
  brief view as relevant).

Acceptance criteria

• The primary title shown is mainTitle[0] (first array element),
  regardless of the UI language
• The subtitle shown next to a title is the one whose language matches
  that title (when it exists)
• Titles in other languages are displayed below the primary title with
  their matching subtitles
• Documents with a single title/language are unaffected
• Consistent behavior between public UI and pro/admin UI

Server: test (sonar.test.rero.ch) — v1.6.0

[PascalRepond]

This does not take into account the fact that the title field is ridiculously complicated (it is an array of objects of arrays of objects)... The language value should be only a the first level. This way, I add one element in the title list for each language used and remove one level of complication.

This is a difficult fix, and it is not worth hacking the display of the field while the structure is incorrect.