diff --git a/frontend/messages/de.json b/frontend/messages/de.json
index ea68718a..9f4dc6ba 100644
--- a/frontend/messages/de.json
+++ b/frontend/messages/de.json
@@ -576,5 +576,33 @@
 	"mission_control_ready_empty_cta": "Jetzt mitmachen",
 	"mission_control_weekly_pulse": "↑ +{count} diese Woche",
 	"mission_control_blocks_progress": "{texted} / {total} Blöcke",
-	"mission_control_reviewed_pct": "{pct}% geprüft"
+	"mission_control_reviewed_pct": "{pct}% geprüft",
+	"error_tag_not_found": "Dieses Schlagwort wurde nicht gefunden.",
+	"error_tag_merge_self": "Ein Schlagwort kann nicht mit sich selbst zusammengeführt werden.",
+	"error_tag_merge_invalid_target": "Das Ziel-Schlagwort ist ein Untergeordnetes des Quell-Schlagworts.",
+	"admin_tag_tree_label": "Schlagwörter",
+	"admin_tag_collapse_node": "Einklappen",
+	"admin_tag_expand_node": "Ausklappen",
+	"admin_tag_parent_placeholder": "Übergeordnetes Schlagwort suchen …",
+	"admin_tag_inherited_color": "Farbe wird von {parent} vererbt",
+	"admin_tag_ancestry_label": "Pfad",
+	"admin_tag_children_label": "Untergeordnete Schlagwörter",
+	"admin_tag_children_more": "… und {count} weitere",
+	"admin_tag_merge_heading": "Zusammenführen",
+	"admin_tag_merge_description": "Alle Dokumente und untergeordnete Schlagwörter auf ein anderes Schlagwort übertragen und dieses danach löschen.",
+	"admin_tag_merge_btn": "Mit anderem Schlagwort zusammenführen …",
+	"admin_tag_merge_target_label": "Ziel-Schlagwort",
+	"admin_tag_merge_preview_docs": "{count} Dokumente",
+	"admin_tag_merge_preview_children": "{count} Untergeordnete",
+	"admin_tag_merge_deleted_after": "wird danach gelöscht",
+	"admin_tag_merge_confirm_btn": "Jetzt zusammenführen",
+	"admin_tag_merge_step1": "Schritt 1 von 2",
+	"admin_tag_merge_step2": "Schritt 2 von 2",
+	"admin_tag_delete_impact": "{docs} Dokument(e) · {descendants} Untergeordnete",
+	"admin_tag_delete_only_this": "Nur dieses Schlagwort löschen",
+	"admin_tag_delete_only_this_sub": "Untergeordnete werden zu {parent} verschoben",
+	"admin_tag_delete_only_this_sub_root": "Untergeordnete werden zu Root-Schlagwörtern",
+	"admin_tag_delete_subtree": "Gesamten Teilbaum löschen",
+	"admin_tag_delete_subtree_warn": "Löscht auch {count} untergeordnete Schlagwörter",
+	"admin_tag_delete_confirm_heading": "Gib «{name}» zur Bestätigung ein:"
 }
diff --git a/frontend/messages/en.json b/frontend/messages/en.json
index 5a91459d..633835f6 100644
--- a/frontend/messages/en.json
+++ b/frontend/messages/en.json
@@ -576,5 +576,33 @@
 	"mission_control_ready_empty_cta": "Start contributing",
 	"mission_control_weekly_pulse": "↑ +{count} this week",
 	"mission_control_blocks_progress": "{texted} / {total} blocks",
-	"mission_control_reviewed_pct": "{pct}% reviewed"
+	"mission_control_reviewed_pct": "{pct}% reviewed",
+	"error_tag_not_found": "This tag was not found.",
+	"error_tag_merge_self": "A tag cannot be merged with itself.",
+	"error_tag_merge_invalid_target": "The target tag is a descendant of the source tag.",
+	"admin_tag_tree_label": "Tags",
+	"admin_tag_collapse_node": "Collapse",
+	"admin_tag_expand_node": "Expand",
+	"admin_tag_parent_placeholder": "Search parent tag …",
+	"admin_tag_inherited_color": "Color inherited from {parent}",
+	"admin_tag_ancestry_label": "Path",
+	"admin_tag_children_label": "Child Tags",
+	"admin_tag_children_more": "… and {count} more",
+	"admin_tag_merge_heading": "Merge",
+	"admin_tag_merge_description": "Transfer all documents and child tags to another tag, then delete this one.",
+	"admin_tag_merge_btn": "Merge with another tag …",
+	"admin_tag_merge_target_label": "Target Tag",
+	"admin_tag_merge_preview_docs": "{count} documents",
+	"admin_tag_merge_preview_children": "{count} children",
+	"admin_tag_merge_deleted_after": "will be deleted after",
+	"admin_tag_merge_confirm_btn": "Merge now",
+	"admin_tag_merge_step1": "Step 1 of 2",
+	"admin_tag_merge_step2": "Step 2 of 2",
+	"admin_tag_delete_impact": "{docs} document(s) · {descendants} child tags",
+	"admin_tag_delete_only_this": "Delete only this tag",
+	"admin_tag_delete_only_this_sub": "Children will be moved to {parent}",
+	"admin_tag_delete_only_this_sub_root": "Children will become root tags",
+	"admin_tag_delete_subtree": "Delete entire subtree",
+	"admin_tag_delete_subtree_warn": "Also deletes {count} child tags",
+	"admin_tag_delete_confirm_heading": "Type «{name}» to confirm:"
 }
diff --git a/frontend/messages/es.json b/frontend/messages/es.json
index d2d09489..fbd52839 100644
--- a/frontend/messages/es.json
+++ b/frontend/messages/es.json
@@ -576,5 +576,33 @@
 	"mission_control_ready_empty_cta": "Empezar a colaborar",
 	"mission_control_weekly_pulse": "↑ +{count} esta semana",
 	"mission_control_blocks_progress": "{texted} / {total} bloques",
-	"mission_control_reviewed_pct": "{pct}% revisado"
+	"mission_control_reviewed_pct": "{pct}% revisado",
+	"error_tag_not_found": "Esta etiqueta no fue encontrada.",
+	"error_tag_merge_self": "Una etiqueta no puede fusionarse consigo misma.",
+	"error_tag_merge_invalid_target": "La etiqueta de destino es descendiente de la etiqueta de origen.",
+	"admin_tag_tree_label": "Etiquetas",
+	"admin_tag_collapse_node": "Colapsar",
+	"admin_tag_expand_node": "Expandir",
+	"admin_tag_parent_placeholder": "Buscar etiqueta superior …",
+	"admin_tag_inherited_color": "Color heredado de {parent}",
+	"admin_tag_ancestry_label": "Ruta",
+	"admin_tag_children_label": "Etiquetas subordinadas",
+	"admin_tag_children_more": "… y {count} más",
+	"admin_tag_merge_heading": "Fusionar",
+	"admin_tag_merge_description": "Transferir todos los documentos y etiquetas subordinadas a otra etiqueta y luego eliminar esta.",
+	"admin_tag_merge_btn": "Fusionar con otra etiqueta …",
+	"admin_tag_merge_target_label": "Etiqueta de destino",
+	"admin_tag_merge_preview_docs": "{count} documentos",
+	"admin_tag_merge_preview_children": "{count} subordinados",
+	"admin_tag_merge_deleted_after": "se eliminará después",
+	"admin_tag_merge_confirm_btn": "Fusionar ahora",
+	"admin_tag_merge_step1": "Paso 1 de 2",
+	"admin_tag_merge_step2": "Paso 2 de 2",
+	"admin_tag_delete_impact": "{docs} documento(s) · {descendants} subordinados",
+	"admin_tag_delete_only_this": "Eliminar solo esta etiqueta",
+	"admin_tag_delete_only_this_sub": "Las subordinadas se moverán a {parent}",
+	"admin_tag_delete_only_this_sub_root": "Las subordinadas se convertirán en etiquetas raíz",
+	"admin_tag_delete_subtree": "Eliminar todo el subárbol",
+	"admin_tag_delete_subtree_warn": "También elimina {count} etiquetas subordinadas",
+	"admin_tag_delete_confirm_heading": "Escribe «{name}» para confirmar:"
 }
diff --git a/frontend/src/lib/errors.ts b/frontend/src/lib/errors.ts
index f712319c..f3979170 100644
--- a/frontend/src/lib/errors.ts
+++ b/frontend/src/lib/errors.ts
@@ -29,6 +29,9 @@ export type ErrorCode =
 	| 'TRAINING_ALREADY_RUNNING'
 	| 'INVALID_TAG_COLOR'
 	| 'TAG_CYCLE_DETECTED'
+	| 'TAG_NOT_FOUND'
+	| 'TAG_MERGE_SELF'
+	| 'TAG_MERGE_INVALID_TARGET'
 	| 'UNAUTHORIZED'
 	| 'FORBIDDEN'
 	| 'VALIDATION_ERROR'
@@ -106,6 +109,12 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_invalid_tag_color();
 		case 'TAG_CYCLE_DETECTED':
 			return m.error_tag_cycle_detected();
+		case 'TAG_NOT_FOUND':
+			return m.error_tag_not_found();
+		case 'TAG_MERGE_SELF':
+			return m.error_tag_merge_self();
+		case 'TAG_MERGE_INVALID_TARGET':
+			return m.error_tag_merge_invalid_target();
 		case 'UNAUTHORIZED':
 			return m.error_unauthorized();
 		case 'FORBIDDEN':