- Add 'language' column to waitlist_entries (en/it/es/fr/de, default en) - Accept 'lang' field in POST /waitlist request body - Translate confirmation email (subject, badge, heading, body, CTA, footer) - Translate confirm/unsubscribe result HTML pages - Return localized success message in WaitlistResponse - Update language preference on duplicate signups - Alembic migration 003_add_language_column