diff --git a/frontend/messages/de.json b/frontend/messages/de.json
index 97f2ad4a..c3692488 100644
--- a/frontend/messages/de.json
+++ b/frontend/messages/de.json
@@ -1046,6 +1046,13 @@
 	"timeline_derived_birth": "Geburt",
 	"timeline_derived_death": "Tod",
 	"timeline_derived_marriage": "Heirat",
+	"timeline_grouping_date": "Gruppierung: Datum",
+	"timeline_provenance_derived": "abgeleitet",
+	"timeline_provenance_curated": "kuratiert",
+	"timeline_letter_glyph_label": "Brief",
+	"timeline_layer_historical_suffix": "historisch",
+	"timeline_strip_density_caption": "Monats-Dichte",
+	"timeline_events_count": "{count} Ereignisse",
 	"event_editor_new_title": "Neues Ereignis",
 	"event_editor_edit_title": "Ereignis bearbeiten",
 	"event_editor_section_when": "Wann",
diff --git a/frontend/messages/en.json b/frontend/messages/en.json
index e0adb2ed..eb3a08ea 100644
--- a/frontend/messages/en.json
+++ b/frontend/messages/en.json
@@ -1046,6 +1046,13 @@
 	"timeline_derived_birth": "Birth",
 	"timeline_derived_death": "Death",
 	"timeline_derived_marriage": "Marriage",
+	"timeline_grouping_date": "Grouping: Date",
+	"timeline_provenance_derived": "derived",
+	"timeline_provenance_curated": "curated",
+	"timeline_letter_glyph_label": "Letter",
+	"timeline_layer_historical_suffix": "historical",
+	"timeline_strip_density_caption": "Monthly density",
+	"timeline_events_count": "{count} events",
 	"event_editor_new_title": "New event",
 	"event_editor_edit_title": "Edit event",
 	"event_editor_section_when": "When",
diff --git a/frontend/messages/es.json b/frontend/messages/es.json
index e67a3578..c2d6df92 100644
--- a/frontend/messages/es.json
+++ b/frontend/messages/es.json
@@ -1046,6 +1046,13 @@
 	"timeline_derived_birth": "Nacimiento",
 	"timeline_derived_death": "Fallecimiento",
 	"timeline_derived_marriage": "Matrimonio",
+	"timeline_grouping_date": "Agrupación: Fecha",
+	"timeline_provenance_derived": "derivado",
+	"timeline_provenance_curated": "curado",
+	"timeline_letter_glyph_label": "Carta",
+	"timeline_layer_historical_suffix": "histórico",
+	"timeline_strip_density_caption": "Densidad mensual",
+	"timeline_events_count": "{count} eventos",
 	"event_editor_new_title": "Nuevo evento",
 	"event_editor_edit_title": "Editar evento",
 	"event_editor_section_when": "Cuándo",
diff --git a/frontend/src/lib/messages.spec.ts b/frontend/src/lib/messages.spec.ts
index 95338e43..3d98c413 100644
--- a/frontend/src/lib/messages.spec.ts
+++ b/frontend/src/lib/messages.spec.ts
@@ -68,4 +68,24 @@ describe('message key parity', () => {
 			timeline_derived_marriage: 'Matrimonio'
 		});
 	});
+
+	// #833 REQ-015: the new visual-fidelity strings (meta line, provenance token,
+	// ✉ label, world-band suffix, density caption) are Paraglide keys present in
+	// every locale so no surface ever falls back to a missing translation.
+	it('zeitstrahl visual-fidelity keys are present in all locales (#833 REQ-015)', () => {
+		const requiredKeys = [
+			'timeline_grouping_date',
+			'timeline_provenance_derived',
+			'timeline_provenance_curated',
+			'timeline_letter_glyph_label',
+			'timeline_layer_historical_suffix',
+			'timeline_strip_density_caption',
+			'timeline_events_count'
+		];
+		for (const key of requiredKeys) {
+			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);
+		}
+	});
 });