Two issues caused the admin sidebar to show a mix of French and English:
1. Only 3 of 14 modules had "menu" translations in their locale files.
When a key was missing, _translate_label() fell back to English Title
Case from the key name — mixing with French from modules that had
translations. Added menu sections to all 4 languages (en, fr, de, lb)
across 13 modules.
2. The language middleware hardcoded admin to "en" ignoring user preference,
while the menu API fell back to DEFAULT_LANGUAGE ("fr") when
preferred_language was NULL. Fixed middleware to respect user's
preferred_language and menu API to use middleware-resolved language
as fallback.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>