diff --git a/frontend/e2e/lang.spec.ts b/frontend/e2e/lang.spec.ts
index b7475e9a..b0efc845 100644
--- a/frontend/e2e/lang.spec.ts
+++ b/frontend/e2e/lang.spec.ts
@@ -58,3 +58,20 @@ test.describe('Language selector', () => {
 		await expect(deBtn).toHaveClass(/font-bold/);
 	});
 });
+
+test.describe('Mobile nav — i18n', () => {
+	test('hamburger button aria-label translates to EN on narrow viewport', async ({ browser }) => {
+		const context = await browser.newContext({
+			viewport: { width: 375, height: 812 },
+			storageState: 'e2e/.auth/user.json'
+		});
+		const page = await context.newPage();
+		await page.goto('/');
+		await page.waitForSelector('[data-hydrated]');
+		await page.getByRole('banner').getByRole('button', { name: 'EN', exact: true }).click();
+
+		await expect(page.getByRole('button', { name: 'Open menu' })).toBeVisible();
+
+		await context.close();
+	});
+});
diff --git a/frontend/messages/de.json b/frontend/messages/de.json
index 72254cf3..dcd08246 100644
--- a/frontend/messages/de.json
+++ b/frontend/messages/de.json
@@ -28,6 +28,8 @@
 	"nav_conversations": "Briefwechsel",
 	"nav_admin": "Admin",
 	"nav_logout": "Abmelden",
+	"layout_menu_open": "Menü öffnen",
+	"layout_menu_close": "Menü schließen",
 	"theme_toggle_to_light": "Zu hellem Design wechseln",
 	"theme_toggle_to_dark": "Zu dunklem Design wechseln",
 	"btn_save": "Speichern",
@@ -394,6 +396,10 @@
 	"doc_panel_discussion_annotation_tab": "Annotation · Seite {page}",
 	"pdf_annotations_show": "Annotierungen anzeigen",
 	"pdf_annotations_hide": "Annotierungen verbergen",
+	"viewer_previous_page": "Zurück",
+	"viewer_next_page": "Weiter",
+	"viewer_zoom_out": "Verkleinern",
+	"viewer_zoom_in": "Vergrößern",
 	"upload_action": "Hochladen",
 	"upload_drop_hint": "Einzeln oder mehrere Dateien auf einmal hochladen",
 	"upload_accepted_types": "PDF, JPEG, PNG, TIFF",
@@ -655,6 +661,7 @@
 	"transcription_block_segmentation_only": "Nur Segmentierung",
 	"training_chip_kurrent": "Kurrent-Erkennung",
 	"training_chip_segmentation": "Segmentierung",
+	"transcribe_mark_for_training": "Für Training vormerken",
 	"training_col_type": "Typ",
 	"training_type_base": "Basis",
 	"training_type_personalized": "Personalisiert",
diff --git a/frontend/messages/en.json b/frontend/messages/en.json
index b8b6dd68..f915633e 100644
--- a/frontend/messages/en.json
+++ b/frontend/messages/en.json
@@ -28,6 +28,8 @@
 	"nav_conversations": "Letters",
 	"nav_admin": "Admin",
 	"nav_logout": "Sign out",
+	"layout_menu_open": "Open menu",
+	"layout_menu_close": "Close menu",
 	"theme_toggle_to_light": "Switch to light mode",
 	"theme_toggle_to_dark": "Switch to dark mode",
 	"btn_save": "Save",
@@ -394,6 +396,10 @@
 	"doc_panel_discussion_annotation_tab": "Annotation · Page {page}",
 	"pdf_annotations_show": "Show annotations",
 	"pdf_annotations_hide": "Hide annotations",
+	"viewer_previous_page": "Previous page",
+	"viewer_next_page": "Next page",
+	"viewer_zoom_out": "Zoom out",
+	"viewer_zoom_in": "Zoom in",
 	"upload_action": "Upload",
 	"upload_drop_hint": "Drop one or multiple files at once",
 	"upload_accepted_types": "PDF, JPEG, PNG, TIFF",
@@ -655,6 +661,7 @@
 	"transcription_block_segmentation_only": "Segmentation only",
 	"training_chip_kurrent": "Kurrent recognition",
 	"training_chip_segmentation": "Segmentation",
+	"transcribe_mark_for_training": "Mark for OCR training",
 	"training_col_type": "Type",
 	"training_type_base": "Base",
 	"training_type_personalized": "Personalized",
diff --git a/frontend/messages/es.json b/frontend/messages/es.json
index 0943943e..1f1dec02 100644
--- a/frontend/messages/es.json
+++ b/frontend/messages/es.json
@@ -28,6 +28,8 @@
 	"nav_conversations": "Cartas",
 	"nav_admin": "Admin",
 	"nav_logout": "Cerrar sesión",
+	"layout_menu_open": "Abrir menú",
+	"layout_menu_close": "Cerrar menú",
 	"theme_toggle_to_light": "Cambiar a modo claro",
 	"theme_toggle_to_dark": "Cambiar a modo oscuro",
 	"btn_save": "Guardar",
@@ -394,6 +396,10 @@
 	"doc_panel_discussion_annotation_tab": "Anotación · Página {page}",
 	"pdf_annotations_show": "Mostrar anotaciones",
 	"pdf_annotations_hide": "Ocultar anotaciones",
+	"viewer_previous_page": "Página anterior",
+	"viewer_next_page": "Página siguiente",
+	"viewer_zoom_out": "Reducir",
+	"viewer_zoom_in": "Ampliar",
 	"upload_action": "Subir",
 	"upload_drop_hint": "Uno o varios archivos a la vez",
 	"upload_accepted_types": "PDF, JPEG, PNG, TIFF",
@@ -655,6 +661,7 @@
 	"transcription_block_segmentation_only": "Solo segmentación",
 	"training_chip_kurrent": "Reconocimiento Kurrent",
 	"training_chip_segmentation": "Segmentación",
+	"transcribe_mark_for_training": "Marcar para entrenamiento de OCR",
 	"training_col_type": "Tipo",
 	"training_type_base": "Base",
 	"training_type_personalized": "Personalizado",
diff --git a/frontend/src/lib/document/transcription/TranscriptionEditView.svelte b/frontend/src/lib/document/transcription/TranscriptionEditView.svelte
index b9aecafe..9aeb473e 100644
--- a/frontend/src/lib/document/transcription/TranscriptionEditView.svelte
+++ b/frontend/src/lib/document/transcription/TranscriptionEditView.svelte
@@ -303,7 +303,9 @@ async function handleLabelToggle(label: string) {
 
 	{#if canWrite && hasBlocks}
 		<div class="border-t border-line px-4 py-3">
-			<p class="mb-2 font-sans text-xs font-medium text-ink-2">Für Training vormerken</p>
+			<p class="mb-2 font-sans text-xs font-medium text-ink-2">
+				{m.transcribe_mark_for_training()}
+			</p>
 			<div class="flex flex-wrap gap-2">
 				{#each [{ label: 'KURRENT_RECOGNITION', display: m.training_chip_kurrent() }, { label: 'KURRENT_SEGMENTATION', display: m.training_chip_segmentation() }] as chip (chip.label)}
 					<button
diff --git a/frontend/src/lib/document/viewer/PdfControls.svelte b/frontend/src/lib/document/viewer/PdfControls.svelte
index f4ff798d..9d99e464 100644
--- a/frontend/src/lib/document/viewer/PdfControls.svelte
+++ b/frontend/src/lib/document/viewer/PdfControls.svelte
@@ -34,7 +34,7 @@ let {
 		<button
 			onclick={onPrev}
 			disabled={currentPage <= 1}
-			aria-label="Zurück"
+			aria-label={m.viewer_previous_page()}
 			class="min-h-[44px] min-w-[44px] rounded p-2 text-ink-3 transition hover:bg-surface/10 focus-visible:ring-2 focus-visible:ring-brand-navy focus-visible:ring-offset-1 disabled:opacity-40"
 		>
 			<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
@@ -51,7 +51,7 @@ let {
 		<button
 			onclick={onNext}
 			disabled={!isLoaded || currentPage >= totalPages}
-			aria-label="Weiter"
+			aria-label={m.viewer_next_page()}
 			class="min-h-[44px] min-w-[44px] rounded p-2 text-ink-3 transition hover:bg-surface/10 focus-visible:ring-2 focus-visible:ring-brand-navy focus-visible:ring-offset-1 disabled:opacity-40"
 		>
 			<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
@@ -64,7 +64,7 @@ let {
 	<div class="flex items-center gap-1">
 		<button
 			onclick={onZoomOut}
-			aria-label="Verkleinern"
+			aria-label={m.viewer_zoom_out()}
 			class="min-h-[44px] min-w-[44px] rounded p-2 text-ink-3 transition hover:bg-surface/10 focus-visible:ring-2 focus-visible:ring-brand-navy focus-visible:ring-offset-1"
 		>
 			<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
@@ -74,7 +74,7 @@ let {
 		</button>
 		<button
 			onclick={onZoomIn}
-			aria-label="Vergrößern"
+			aria-label={m.viewer_zoom_in()}
 			class="min-h-[44px] min-w-[44px] rounded p-2 text-ink-3 transition hover:bg-surface/10 focus-visible:ring-2 focus-visible:ring-brand-navy focus-visible:ring-offset-1"
 		>
 			<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
diff --git a/frontend/src/lib/document/viewer/PdfControls.svelte.spec.ts b/frontend/src/lib/document/viewer/PdfControls.svelte.spec.ts
index 6dadc3ac..a6a56d8d 100644
--- a/frontend/src/lib/document/viewer/PdfControls.svelte.spec.ts
+++ b/frontend/src/lib/document/viewer/PdfControls.svelte.spec.ts
@@ -2,6 +2,7 @@ import { vi, describe, it, expect, afterEach } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page } from 'vitest/browser';
 
+import { m } from '$lib/paraglide/messages.js';
 import PdfControls from './PdfControls.svelte';
 
 afterEach(cleanup);
@@ -23,28 +24,28 @@ describe('PdfControls — annotation toggle visibility', () => {
 	it('renders annotation toggle when annotationCount is greater than zero', async () => {
 		render(PdfControls, { ...defaultProps, annotationCount: 3 });
 		await expect
-			.element(page.getByRole('button', { name: /annotierungen anzeigen/i }))
+			.element(page.getByRole('button', { name: m.pdf_annotations_show() }))
 			.toBeInTheDocument();
 	});
 
 	it('does not render annotation toggle when annotationCount is zero', async () => {
 		render(PdfControls, { ...defaultProps, annotationCount: 0 });
 		await expect
-			.element(page.getByRole('button', { name: /annotierungen/i }))
+			.element(page.getByRole('button', { name: m.pdf_annotations_show() }))
 			.not.toBeInTheDocument();
 	});
 });
 
 describe('PdfControls — annotation toggle label', () => {
-	it('shows "Annotierungen anzeigen" label when annotations are hidden', async () => {
+	it('shows show-annotations label when annotations are hidden', async () => {
 		render(PdfControls, { ...defaultProps, annotationCount: 2, showAnnotations: false });
-		const btn = page.getByRole('button', { name: /annotierungen anzeigen/i });
+		const btn = page.getByRole('button', { name: m.pdf_annotations_show() });
 		await expect.element(btn).toBeInTheDocument();
 	});
 
-	it('shows "Annotierungen verbergen" label when annotations are visible', async () => {
+	it('shows hide-annotations label when annotations are visible', async () => {
 		render(PdfControls, { ...defaultProps, annotationCount: 2, showAnnotations: true });
-		const btn = page.getByRole('button', { name: /annotierungen verbergen/i });
+		const btn = page.getByRole('button', { name: m.pdf_annotations_hide() });
 		await expect.element(btn).toBeInTheDocument();
 	});
 });
@@ -58,7 +59,9 @@ describe('PdfControls — annotation toggle contrast (WCAG 2.1 AA)', () => {
 		});
 		const allButtons = container.querySelectorAll('button');
 		const annotationBtn = Array.from(allButtons).find((b) =>
-			b.getAttribute('aria-label')?.toLowerCase().includes('annotierungen')
+			[m.pdf_annotations_show(), m.pdf_annotations_hide()].includes(
+				b.getAttribute('aria-label') ?? ''
+			)
 		);
 		expect(annotationBtn).not.toBeNull();
 		expect(annotationBtn!.className).toContain('text-primary');
@@ -75,7 +78,9 @@ describe('PdfControls — focus rings (WCAG 2.1 §2.4.7)', () => {
 		});
 		const allButtons = container.querySelectorAll('button');
 		const annotationBtn = Array.from(allButtons).find((b) =>
-			b.getAttribute('aria-label')?.toLowerCase().includes('annotierungen')
+			[m.pdf_annotations_show(), m.pdf_annotations_hide()].includes(
+				b.getAttribute('aria-label') ?? ''
+			)
 		);
 		expect(annotationBtn).not.toBeNull();
 		expect(annotationBtn!.className).toContain('focus-visible:ring-2');
@@ -86,7 +91,12 @@ describe('PdfControls — focus rings (WCAG 2.1 §2.4.7)', () => {
 		const allButtons = container.querySelectorAll('button');
 		const iconOnlyButtons = Array.from(allButtons).filter((b) => {
 			const label = b.getAttribute('aria-label') ?? '';
-			return ['zurück', 'weiter', 'verkleinern', 'vergrößern'].includes(label.toLowerCase());
+			return [
+				m.viewer_previous_page(),
+				m.viewer_next_page(),
+				m.viewer_zoom_out(),
+				m.viewer_zoom_in()
+			].includes(label);
 		});
 		expect(iconOnlyButtons).toHaveLength(4);
 		for (const btn of iconOnlyButtons) {
@@ -104,7 +114,9 @@ describe('PdfControls — touch targets (WCAG 2.2 §2.5.8)', () => {
 		});
 		const allButtons = container.querySelectorAll('button');
 		const annotationBtn = Array.from(allButtons).find((b) =>
-			b.getAttribute('aria-label')?.toLowerCase().includes('annotierungen')
+			[m.pdf_annotations_show(), m.pdf_annotations_hide()].includes(
+				b.getAttribute('aria-label') ?? ''
+			)
 		);
 		expect(annotationBtn).not.toBeNull();
 		expect(annotationBtn!.className).toContain('min-h-[44px]');
@@ -118,7 +130,9 @@ describe('PdfControls — touch targets (WCAG 2.2 §2.5.8)', () => {
 		});
 		const allButtons = container.querySelectorAll('button');
 		const annotationBtn = Array.from(allButtons).find((b) =>
-			b.getAttribute('aria-label')?.toLowerCase().includes('annotierungen')
+			[m.pdf_annotations_show(), m.pdf_annotations_hide()].includes(
+				b.getAttribute('aria-label') ?? ''
+			)
 		);
 		expect(annotationBtn).not.toBeNull();
 		expect(annotationBtn!.className).toContain('min-w-[44px]');
@@ -131,7 +145,9 @@ describe('PdfControls — touch targets (WCAG 2.2 §2.5.8)', () => {
 			showAnnotations: false
 		});
 		const btn1 = Array.from(c1.querySelectorAll('button')).find((b) =>
-			b.getAttribute('aria-label')?.toLowerCase().includes('annotierungen')
+			[m.pdf_annotations_show(), m.pdf_annotations_hide()].includes(
+				b.getAttribute('aria-label') ?? ''
+			)
 		);
 		expect(btn1!.getAttribute('aria-pressed')).toBe('false');
 		cleanup();
@@ -142,7 +158,9 @@ describe('PdfControls — touch targets (WCAG 2.2 §2.5.8)', () => {
 			showAnnotations: true
 		});
 		const btn2 = Array.from(c2.querySelectorAll('button')).find((b) =>
-			b.getAttribute('aria-label')?.toLowerCase().includes('annotierungen')
+			[m.pdf_annotations_show(), m.pdf_annotations_hide()].includes(
+				b.getAttribute('aria-label') ?? ''
+			)
 		);
 		expect(btn2!.getAttribute('aria-pressed')).toBe('true');
 	});
@@ -152,7 +170,12 @@ describe('PdfControls — touch targets (WCAG 2.2 §2.5.8)', () => {
 		const allButtons = container.querySelectorAll('button');
 		const iconOnlyButtons = Array.from(allButtons).filter((b) => {
 			const label = b.getAttribute('aria-label') ?? '';
-			return ['zurück', 'weiter', 'verkleinern', 'vergrößern'].includes(label.toLowerCase());
+			return [
+				m.viewer_previous_page(),
+				m.viewer_next_page(),
+				m.viewer_zoom_out(),
+				m.viewer_zoom_in()
+			].includes(label);
 		});
 		expect(iconOnlyButtons).toHaveLength(4);
 		for (const btn of iconOnlyButtons) {
@@ -165,7 +188,12 @@ describe('PdfControls — touch targets (WCAG 2.2 §2.5.8)', () => {
 		const allButtons = container.querySelectorAll('button');
 		const iconOnlyButtons = Array.from(allButtons).filter((b) => {
 			const label = b.getAttribute('aria-label') ?? '';
-			return ['zurück', 'weiter', 'verkleinern', 'vergrößern'].includes(label.toLowerCase());
+			return [
+				m.viewer_previous_page(),
+				m.viewer_next_page(),
+				m.viewer_zoom_out(),
+				m.viewer_zoom_in()
+			].includes(label);
 		});
 		expect(iconOnlyButtons).toHaveLength(4);
 		for (const btn of iconOnlyButtons) {
diff --git a/frontend/src/lib/messages.spec.ts b/frontend/src/lib/messages.spec.ts
new file mode 100644
index 00000000..e6d0b96c
--- /dev/null
+++ b/frontend/src/lib/messages.spec.ts
@@ -0,0 +1,43 @@
+import { describe, it, expect } from 'vitest';
+import de from '../../messages/de.json';
+import en from '../../messages/en.json';
+import es from '../../messages/es.json';
+
+describe('message key parity', () => {
+	it('de, en, and es have identical key sets', () => {
+		const deKeys = Object.keys(de).sort();
+		const enKeys = Object.keys(en).sort();
+		const esKeys = Object.keys(es).sort();
+		expect(enKeys).toEqual(deKeys);
+		expect(esKeys).toEqual(deKeys);
+	});
+
+	it('viewer navigation keys are present in all locales', () => {
+		const requiredViewerKeys = [
+			'viewer_previous_page',
+			'viewer_next_page',
+			'viewer_zoom_out',
+			'viewer_zoom_in'
+		];
+		for (const key of requiredViewerKeys) {
+			expect(de, `missing key in de: ${key}`).toHaveProperty(key);
+			expect(en, `missing key in en: ${key}`).toHaveProperty(key);
+			expect(es, `missing key in es: ${key}`).toHaveProperty(key);
+		}
+	});
+
+	it('transcribe mark-for-training key is present in all locales', () => {
+		expect(de).toHaveProperty('transcribe_mark_for_training');
+		expect(en).toHaveProperty('transcribe_mark_for_training');
+		expect(es).toHaveProperty('transcribe_mark_for_training');
+	});
+
+	it('layout menu open/close keys are present in all locales', () => {
+		expect(de).toHaveProperty('layout_menu_open');
+		expect(de).toHaveProperty('layout_menu_close');
+		expect(en).toHaveProperty('layout_menu_open');
+		expect(en).toHaveProperty('layout_menu_close');
+		expect(es).toHaveProperty('layout_menu_open');
+		expect(es).toHaveProperty('layout_menu_close');
+	});
+});
diff --git a/frontend/src/routes/AppNav.svelte b/frontend/src/routes/AppNav.svelte
index 344bb207..260c96c8 100644
--- a/frontend/src/routes/AppNav.svelte
+++ b/frontend/src/routes/AppNav.svelte
@@ -94,7 +94,7 @@ function handleOverlayKeydown(event: KeyboardEvent) {
 	<!-- Hamburger toggle (mobile only) -->
 	<button
 		class="ml-auto flex h-11 w-11 items-center justify-center self-center rounded text-white/70 transition-colors hover:bg-white/10 hover:text-white focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring lg:hidden"
-		aria-label={mobileNavOpen ? 'Menü schließen' : 'Menü öffnen'}
+		aria-label={mobileNavOpen ? m.layout_menu_close() : m.layout_menu_open()}
 		aria-expanded={mobileNavOpen}
 		aria-controls="mobile-nav"
 		onclick={() => (mobileNavOpen = !mobileNavOpen)}