Add Scandinavian i18n (da/sv/nb) via DeepL pipeline.

Integrate new locale bundles, language cycling in the UI, SEO hreflang tags, and localized beta flyer HTML variants with scripts for batch translation and key validation.

Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/components/InvitationAcceptance.tsx

@@ -1,5 +1,6 @@
 import React, { useState, useEffect, useCallback, useRef } from 'react'
 import { useTranslation } from 'react-i18next'
+import { getNextLanguage } from '../utils/i18nLanguages.js'
 import { Ship, LogIn, UserPlus, AlertTriangle, ShieldCheck, Languages, ArrowRight, KeyRound } from 'lucide-react'
 import {
   getActiveMasterKey,
@@ -308,7 +309,7 @@ export default function InvitationAcceptance({ onAccepted, onCancel }: Invitatio
   }
 
   const toggleLanguage = () => {
-    i18n.changeLanguage(i18n.language.startsWith('de') ? 'en' : 'de')
+    i18n.changeLanguage(getNextLanguage(i18n.language))
   }
 
   if (recoveryPhrase) {
@@ -511,7 +512,7 @@ export default function InvitationAcceptance({ onAccepted, onCancel }: Invitatio
       <div className="auth-footer" style={{ borderTop: '1px solid rgba(255,255,255,0.05)', paddingTop: '16px', marginTop: '24px' }}>
         <button className="btn-icon-text" onClick={toggleLanguage}>
           <Languages size={18} />
-          {i18n.language.startsWith('de') ? t('invitation.switch_language_en') : t('invitation.switch_language_de')}
+          {t(`languages.${getNextLanguage(i18n.language)}`)}
         </button>
       </div>
     </div>