[4/5] i18n + accessibility integration for Unified Settings modal (Share tab) and language preselect

[mfittko]

Parent: #7

Scope
Integrate translations and accessibility into the Unified Settings modal (Share tab), and ensure language preselection works via lang parameter.

Deliverables (updated)

• New translation keys in src/locales/{en,de,fr,es}.json
• Wire the language dropdown to i18n provider; unsupported lang falls back to default
• ARIA labels and keyboard navigability for all new controls in the modal
• Visual QA: hidden controls should not leave gaps

Details and context

• PRD Sections 6, 9
• Task List Task 4.0

Acceptance Criteria

• Language switching reflects immediately in UI
• All controls pass basic axe-like checks (labels, roles)

[mfittko]

Resolving this sub-issue via PR #15.

Status against deliverables:

• Translations: Added and wired for the Unified Settings modal across en/de/es/fr.
• Language preselect: ?lang= is parsed and applied pre-render; Share tab’s language selector affects shared URLs, while the General tab’s selector changes the current UI language immediately.
• Accessibility: Controls in the Share tab (and the rest of the modal) have labels and are keyboard-navigable (Label↔control associations; dialog/tabs from shadcn handle focus management).
• Visual QA: Conditional rendering prevents layout gaps when options are hidden.

Scope clarification (behavior split):

• General tab language → immediate UI language change.
• Share tab language → language for generated shared URLs only.

With the above implemented in PR #15, this issue is complete. Closing. If anything remains, please reopen or create a follow-up.

Reference: Issue #11