diff --git a/client/src/App.tsx b/client/src/App.tsx
index 57dfbec..1d4e337 100644
--- a/client/src/App.tsx
+++ b/client/src/App.tsx
@@ -45,7 +45,7 @@ import { Ship, LogOut, ChevronLeft, Users, FileText, Settings, Wifi, WifiOff, La
 import DisclaimerHeaderButton from './components/DisclaimerHeaderButton.tsx'
 import FeedbackHeaderButton from './components/FeedbackHeaderButton.tsx'
 import { useTranslation } from 'react-i18next'
-import { getNextLanguage } from './utils/i18nLanguages.js'
+import { cycleAppLanguage } from './utils/i18nLanguages.js'
 import {
   resolveTourLogbookContext,
   seedDemoLogbookIfNeeded
@@ -497,7 +497,7 @@ function App() {
   }
 
   const toggleLanguage = () => {
-    i18n.changeLanguage(getNextLanguage(i18n.language))
+    cycleAppLanguage(i18n)
   }
 
   const handleExitDemo = () => {
diff --git a/client/src/components/AuthOnboarding.tsx b/client/src/components/AuthOnboarding.tsx
index 9800efa..784b35e 100644
--- a/client/src/components/AuthOnboarding.tsx
+++ b/client/src/components/AuthOnboarding.tsx
@@ -1,6 +1,6 @@
 import React, { useState } from 'react'
 import { useTranslation } from 'react-i18next'
-import { getNextLanguage } from '../utils/i18nLanguages.js'
+import { cycleAppLanguage, getNextLanguage } from '../utils/i18nLanguages.js'
 import { 
   registerUser, 
   loginUser, 
@@ -210,7 +210,7 @@ export default function AuthOnboarding({ onAuthenticated, onOpenDemo }: AuthOnbo
   }
 
   const toggleLanguage = () => {
-    i18n.changeLanguage(getNextLanguage(i18n.language))
+    cycleAppLanguage(i18n)
   }
 
   const copyToClipboard = () => {
diff --git a/client/src/components/DemoViewer.tsx b/client/src/components/DemoViewer.tsx
index d6e6445..ef64a04 100644
--- a/client/src/components/DemoViewer.tsx
+++ b/client/src/components/DemoViewer.tsx
@@ -1,6 +1,6 @@
 import { useState, useEffect } from 'react'
 import { useTranslation } from 'react-i18next'
-import { getNextLanguage } from '../utils/i18nLanguages.js'
+import { cycleAppLanguage, getNextLanguage } from '../utils/i18nLanguages.js'
 import VesselForm from './VesselForm.tsx'
 import CrewForm from './CrewForm.tsx'
 import LogEntriesList from './LogEntriesList.tsx'
@@ -49,7 +49,7 @@ export default function DemoViewer({ onExit }: DemoViewerProps) {
   }, [registerNavigation, registerDemoTourContext, startTour, fixture.firstEntryId])
 
   const toggleLanguage = () => {
-    i18n.changeLanguage(getNextLanguage(i18n.language))
+    cycleAppLanguage(i18n)
   }
 
   const { title, yacht, crews, entries, gpsTracks, photos, firstEntryId } = fixture
diff --git a/client/src/components/InvitationAcceptance.tsx b/client/src/components/InvitationAcceptance.tsx
index 702ee7a..4677683 100644
--- a/client/src/components/InvitationAcceptance.tsx
+++ b/client/src/components/InvitationAcceptance.tsx
@@ -1,6 +1,6 @@
 import React, { useState, useEffect, useCallback, useRef } from 'react'
 import { useTranslation } from 'react-i18next'
-import { getNextLanguage } from '../utils/i18nLanguages.js'
+import { cycleAppLanguage, getNextLanguage } from '../utils/i18nLanguages.js'
 import { Ship, LogIn, UserPlus, AlertTriangle, ShieldCheck, Languages, ArrowRight, KeyRound } from 'lucide-react'
 import {
   getActiveMasterKey,
@@ -309,7 +309,7 @@ export default function InvitationAcceptance({ onAccepted, onCancel }: Invitatio
   }
 
   const toggleLanguage = () => {
-    i18n.changeLanguage(getNextLanguage(i18n.language))
+    cycleAppLanguage(i18n)
   }
 
   if (recoveryPhrase) {
diff --git a/client/src/components/LogbookDashboard.tsx b/client/src/components/LogbookDashboard.tsx
index 3324309..fddf242 100644
--- a/client/src/components/LogbookDashboard.tsx
+++ b/client/src/components/LogbookDashboard.tsx
@@ -1,6 +1,6 @@
 import React, { useState, useEffect, useRef, useMemo } from 'react'
 import { useTranslation } from 'react-i18next'
-import { getNextLanguage } from '../utils/i18nLanguages.js'
+import { cycleAppLanguage } from '../utils/i18nLanguages.js'
 import { useSyncIndicator } from '../hooks/useSyncIndicator.js'
 import { fetchLogbooks, createLogbook, deleteLogbook, updateLogbookTitle, type DecryptedLogbook } from '../services/logbook.js'
 import LogbookRoleBadge from './LogbookRoleBadge.tsx'
@@ -194,7 +194,7 @@ export default function LogbookDashboard({ onSelectLogbook, onLogout, onOpenProf
   }
 
   const toggleLanguage = () => {
-    i18n.changeLanguage(getNextLanguage(i18n.language))
+    cycleAppLanguage(i18n)
   }
 
   const ownedLogbooks = logbooks.filter((lb) => !lb.isShared)
diff --git a/client/src/components/ReadOnlyViewer.tsx b/client/src/components/ReadOnlyViewer.tsx
index 220b72f..3c07504 100644
--- a/client/src/components/ReadOnlyViewer.tsx
+++ b/client/src/components/ReadOnlyViewer.tsx
@@ -1,6 +1,6 @@
 import { useState, useEffect } from 'react'
 import { useTranslation } from 'react-i18next'
-import { getNextLanguage, isGermanLocale } from '../utils/i18nLanguages.js'
+import { cycleAppLanguage, getNextLanguage, isGermanLocale } from '../utils/i18nLanguages.js'
 import { decryptJson } from '../services/crypto.js'
 import { PlausibleEvents, trackPlausibleEvent } from '../services/analytics.js'
 import VesselForm from './VesselForm.tsx'
@@ -137,7 +137,7 @@ export default function ReadOnlyViewer({ token, hexKey }: ReadOnlyViewerProps) {
   }
 
   const toggleLanguage = () => {
-    i18n.changeLanguage(getNextLanguage(i18n.language))
+    cycleAppLanguage(i18n)
   }
 
   if (loading) {
diff --git a/client/src/services/analytics.ts b/client/src/services/analytics.ts
index 3260745..d8a23c0 100644
--- a/client/src/services/analytics.ts
+++ b/client/src/services/analytics.ts
@@ -34,7 +34,8 @@ export const PlausibleEvents = {
   LOCAL_PIN_SET: 'Local PIN Set',
   LOCAL_PIN_REMOVED: 'Local PIN Removed',
   DEVICE_FORGOTTEN: 'Device Forgotten',
-  RECOVERY_ROTATED: 'Recovery Rotated'
+  RECOVERY_ROTATED: 'Recovery Rotated',
+  LANGUAGE_CHANGED: 'Language Changed'
 } as const
 
 export type PlausibleEventName = (typeof PlausibleEvents)[keyof typeof PlausibleEvents]
diff --git a/client/src/utils/i18nLanguages.test.ts b/client/src/utils/i18nLanguages.test.ts
index cdf3050..36819e7 100644
--- a/client/src/utils/i18nLanguages.test.ts
+++ b/client/src/utils/i18nLanguages.test.ts
@@ -1,7 +1,40 @@
-import { describe, expect, it } from 'vitest'
-import { getNextLanguage, normalizeAppLanguage, SUPPORTED_LANGUAGES } from './i18nLanguages.js'
+import type { i18n as I18nInstance } from 'i18next'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+import { PlausibleEvents } from '../services/analytics.js'
+import {
+  changeAppLanguage,
+  cycleAppLanguage,
+  getNextLanguage,
+  normalizeAppLanguage,
+  SUPPORTED_LANGUAGES
+} from './i18nLanguages.js'
+
+const trackPlausibleEvent = vi.fn()
+
+vi.mock('../services/analytics.js', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('../services/analytics.js')>()
+  return {
+    ...actual,
+    trackPlausibleEvent: (...args: unknown[]) => trackPlausibleEvent(...args)
+  }
+})
+
+function createMockI18n(language: string): I18nInstance {
+  let current = language
+  return {
+    language: current,
+    changeLanguage: vi.fn(async (lng: string) => {
+      current = lng
+      ;(this as { language: string }).language = lng
+    })
+  } as unknown as I18nInstance
+}
 
 describe('i18nLanguages', () => {
+  beforeEach(() => {
+    trackPlausibleEvent.mockReset()
+  })
+
   it('normalizes regional tags to supported base codes', () => {
     expect(normalizeAppLanguage('de-DE')).toBe('de')
     expect(normalizeAppLanguage('nb-NO')).toBe('nb')
@@ -18,4 +51,33 @@ describe('i18nLanguages', () => {
     expect(seen.size).toBe(SUPPORTED_LANGUAGES.length)
     expect(current).toBe('de')
   })
+
+  it('tracks explicit language changes', () => {
+    const i18n = createMockI18n('de')
+    changeAppLanguage(i18n, 'sv')
+
+    expect(i18n.changeLanguage).toHaveBeenCalledWith('sv')
+    expect(trackPlausibleEvent).toHaveBeenCalledWith(PlausibleEvents.LANGUAGE_CHANGED, {
+      from: 'de',
+      to: 'sv'
+    })
+  })
+
+  it('does not track when language stays the same', () => {
+    const i18n = createMockI18n('en')
+    changeAppLanguage(i18n, 'en')
+
+    expect(i18n.changeLanguage).not.toHaveBeenCalled()
+    expect(trackPlausibleEvent).not.toHaveBeenCalled()
+  })
+
+  it('cycleAppLanguage tracks the next language', () => {
+    const i18n = createMockI18n('nb')
+    cycleAppLanguage(i18n)
+
+    expect(trackPlausibleEvent).toHaveBeenCalledWith(PlausibleEvents.LANGUAGE_CHANGED, {
+      from: 'nb',
+      to: 'de'
+    })
+  })
 })
diff --git a/client/src/utils/i18nLanguages.ts b/client/src/utils/i18nLanguages.ts
index f7f15ea..cf0e985 100644
--- a/client/src/utils/i18nLanguages.ts
+++ b/client/src/utils/i18nLanguages.ts
@@ -1,3 +1,6 @@
+import type { i18n as I18nInstance } from 'i18next'
+import { PlausibleEvents, trackPlausibleEvent } from '../services/analytics.js'
+
 /** Supported UI languages (ISO 639-1, language-only). */
 export const SUPPORTED_LANGUAGES = ['de', 'en', 'da', 'sv', 'nb'] as const
 
@@ -20,3 +23,17 @@ export function getNextLanguage(current?: string): AppLanguage {
 export function isGermanLocale(language?: string): boolean {
   return normalizeAppLanguage(language) === 'de'
 }
+
+/** Switch UI language and track explicit user choice (not auto-detection). */
+export function changeAppLanguage(i18n: I18nInstance, language: AppLanguage): void {
+  const from = normalizeAppLanguage(i18n.language)
+  const to = normalizeAppLanguage(language)
+  if (from === to) return
+
+  void i18n.changeLanguage(to)
+  trackPlausibleEvent(PlausibleEvents.LANGUAGE_CHANGED, { from, to })
+}
+
+export function cycleAppLanguage(i18n: I18nInstance): void {
+  changeAppLanguage(i18n, getNextLanguage(i18n.language))
+}
diff --git a/docs/plausible-events.md b/docs/plausible-events.md
index 96b30de..6696bed 100644
--- a/docs/plausible-events.md
+++ b/docs/plausible-events.md
@@ -49,6 +49,7 @@ Kapteins Daagbok nutzt [Plausible Analytics](https://plausible.io/) mit dem Scri
 | Local PIN Removed | Lokaler PIN entfernt (`UserProfilePage.tsx`) | — |
 | Device Forgotten | Account aus Schnell-Login-Liste dieses Geräts entfernt (`UserProfilePage.tsx`) | — |
 | Recovery Rotated | Neuer 12-Wörter-Wiederherstellungsschlüssel erstellt (`UserProfilePage.tsx`) | — |
+| Language Changed | Sprache über UI-Wechsler gewählt (`i18nLanguages.ts` via Sprach-Button in App, Dashboard, Auth, Demo, Einladung, Share-Viewer) | `from`, `to`: ISO 639-1 (`de`, `en`, `da`, `sv`, `nb`) |
 
 ## Bewusst nicht getrackt
 
@@ -56,6 +57,7 @@ Kapteins Daagbok nutzt [Plausible Analytics](https://plausible.io/) mit dem Scri
 - **Manuelle Signaturen:** Nur Passkey-Signaturen lösen `Entry Signed` aus.
 - **PII:** Keine Inhalte aus verschlüsselten Logbüchern in Properties.
 - **Profil-KPIs:** Statistik-Karten und User-ID-Kopieren werden nicht getrackt (reine Anzeige bzw. zu granular).
+- **Sprache bei Erstbesuch:** Automatische Browser-/URL-Erkennung (`i18next-browser-languagedetector`, `?lng=`) löst kein `Language Changed` aus — nur explizite Klicks auf den Sprach-Button.
 - **Kontolöschung:** `Account Deleted` bleibt in `auth.ts` — unabhängig davon, ob die Gefahrenzone auf der Profilseite oder früher in den Einstellungen genutzt wurde.
 
 ## Typische Funnels (Plausible Goals)
@@ -69,6 +71,7 @@ Empfohlene Goal-Ketten für Auswertung:
 5. **Export:** Travel Day Saved → PDF Exported / CSV Exported
 6. **Datensicherung:** Backup Exported → Backup Restored
 7. **Kontosicherheit:** Profile Opened → Passkey Added / Local PIN Set / Recovery Rotated; Last Passkey Remove Hinted → Account Deleted (selten, aber aussagekräftig)
+8. **Internationalisierung:** Language Changed (Verteilung `to`, Pfade mit Übersetzungs-Feedback)
 
 ## Entwicklung
 
@@ -77,6 +80,7 @@ import { PlausibleEvents, trackPlausibleEvent } from './services/analytics.js'
 
 trackPlausibleEvent(PlausibleEvents.TRAVEL_DAY_SAVED)
 trackPlausibleEvent(PlausibleEvents.ENTRY_SIGNED, { role: 'skipper' })
+trackPlausibleEvent(PlausibleEvents.LANGUAGE_CHANGED, { from: 'de', to: 'da' })
 ```
 
 Lokal ohne Plausible-Script ist `trackPlausibleEvent` ein No-Op. In Production im Browser-Netzwerk-Tab auf Requests an die Plausible-Instanz prüfen.