feat(SPA): i18n internationzalization, english and french

features/spa_internationalization.feature

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+Feature: English and French throughout the SPA
+
+  Background:
+    Given all existing SPA interface text supports English and French
+    And English preserves existing copy and French provides equivalent meaning
+    And user content, API data and transactional emails remain unchanged
+    And visual checks are waived by the user for this slice
+    And the language control uses existing design tokens
+
+  Scenario Outline: Resolve the language before rendering
+    Given the browser-local stored language is <stored>
+    When the SPA starts
+    Then the interface language and document lang are <locale>
+    And browser language does not override the choice
+
+    Examples:
+      | stored      | locale |
+      | absent      | en     |
+      | en          | en     |
+      | fr          | fr     |
+      | unsupported | en     |
+      | unreadable  | en     |
+
+  Scenario Outline: Open the language picker in the profile submenu
+    Given the user opens the <menu>
+    When they activate the localized Language control
+    Then a compact scrollable picker offers English and Français
+    And the selected language is visibly and accessibly identified
+    And the picker uses Nuxt UI and existing design tokens
+
+    Examples:
+      | menu                    |
+      | desktop UserMenu        |
+      | mobile AccountMenuSheet |
+
+  Scenario: Switch language without losing work
+    Given the user is editing an unsaved display name on /profile
+    When they select Français
+    Then all SPA interface text immediately uses French
+    And the document lang is fr
+    And the route, session, theme and unsaved work remain unchanged
+    And no reload, navigation or API request is caused by switching
+    When they select English
+    Then the interface immediately restores English with the same preserved state
+
+  Scenario: Remember language on this browser
+    Given the user selected Français
+    When they navigate, reload, log out or return on this browser
+    Then French remains selected including on public authentication screens
+    And no language preference is sent to the server
+
+  Scenario: Storage failure does not prevent switching
+    Given preference storage cannot be written
+    When the user selects Français
+    Then French is used for the current session without an error
+    And a fresh load without a readable preference defaults to English
+
+  Scenario: Translate the entire interface
+    Given French is selected
+    When an existing SPA screen or shared component renders
+    Then navigation, forms, validation, notifications, dialogs and accessibility labels use French
+    And counts, human-readable dates and numbers use the selected locale
+    And Nuxt UI controls use the selected locale
+    And English and French catalogs have matching keys and interpolation parameters
+    And an unavailable French message falls back to English
+    And user content, account details, filenames, URLs, API data and emails remain unchanged
+
+  Scenario Outline: Operate the picker accessibly
+    Given the picker is open in the <menu>
+    When the user navigates its options with the keyboard and confirms a choice
+    Then the language changes and the picker closes
+    And focus returns to its language control
+    When they reopen it and press Escape or click outside
+    Then the picker closes without changing language
+
+    Examples:
+      | menu                    |
+      | desktop UserMenu        |
+      | mobile AccountMenuSheet |

features/spa_internationalization.qa.md

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+# SPA internationalization QA
+
+Accepted by the user on 2026-10-03 together with the slice specification.
+
+## Automated
+
+1. Verify absent, English, French, unsupported and unreadable stored preferences; English defaults independently of browser language and document lang follows selection.
+2. Verify desktop UserMenu and mobile AccountMenuSheet offer a localized language entry and a compact bounded scrollable picker with English and Français, selected-state semantics, selection, dismissal and focus return. Preserve profile, theme and logout behavior.
+3. Switch both ways while editing an unsaved profile display name. Verify translated UI and unchanged draft, route, session and theme without additional API requests.
+4. Verify browser-local persistence across reload initialization, navigation and logout/public authentication. Verify storage write failure allows switching for the current session.
+5. Preserve existing English tests and add French checks for login, validation, profile save failure, integration copy feedback, not-found, representative dialogs and notifications.
+6. Audit every existing view, shared component, composable and library producing interface text, including editor, media, users, invitations, settings and updates. Verify Nuxt UI controls use the active locale.
+7. Assert catalog key/interpolation parity, nonempty translations, pluralization, English fallback and locale-sensitive formatting. Use fixed input dates without freezing system time. Verify displayed alerts and dialogs react to language changes.
+8. Verify user content, account details, filenames, URLs, API fields, integration protocol examples, server release notes and transactional emails remain unchanged.
+9. Run task test:web, frontend type checks, applicable lint and final build checks. Inspect introduced comments and ensure application changes are SPA-only.
+
+## Visual and manual
+
+Visual checks are SKIPPED by explicit user waiver for this slice because the designer is unavailable. The user authorized a coherent language control using existing design tokens. Do not edit design sources or claim pixel parity.
+
+Manual checklist: desktop/mobile and light/dark coherence, viewport containment, constrained scrolling, French text readability, touch and mouse selection, keyboard movement and confirmation, Escape/outside dismissal, focus return and visible focus. Confirm language retention after reload and logout. Do not freeze dates or investigate clock-sensitive states.