diff --git a/frontend/src/lib/messages.spec.ts b/frontend/src/lib/messages.spec.ts
index e6d0b96c..95338e43 100644
--- a/frontend/src/lib/messages.spec.ts
+++ b/frontend/src/lib/messages.spec.ts
@@ -40,4 +40,32 @@ describe('message key parity', () => {
 		expect(es).toHaveProperty('layout_menu_open');
 		expect(es).toHaveProperty('layout_menu_close');
 	});
+
+	// REQ-024: the timeline layer/life-event labels feed sr-only / aria text, so
+	// they are localized per locale (the original German-only MVP decision was
+	// reversed for accessibility). Pin the values so en/es can never silently
+	// drift back to the German source strings.
+	it('timeline layer/derived labels are localized per locale (REQ-024)', () => {
+		expect(de).toMatchObject({
+			timeline_layer_world: 'Weltgeschehen',
+			timeline_layer_family: 'Familie',
+			timeline_derived_birth: 'Geburt',
+			timeline_derived_death: 'Tod',
+			timeline_derived_marriage: 'Heirat'
+		});
+		expect(en).toMatchObject({
+			timeline_layer_world: 'World events',
+			timeline_layer_family: 'Family',
+			timeline_derived_birth: 'Birth',
+			timeline_derived_death: 'Death',
+			timeline_derived_marriage: 'Marriage'
+		});
+		expect(es).toMatchObject({
+			timeline_layer_world: 'Acontecimientos mundiales',
+			timeline_layer_family: 'Familia',
+			timeline_derived_birth: 'Nacimiento',
+			timeline_derived_death: 'Fallecimiento',
+			timeline_derived_marriage: 'Matrimonio'
+		});
+	});
 });