diff --git a/Source/Modules/PrefMgr_Extension.swift b/Source/Modules/PrefMgr_Extension.swift
index f09ce4f3..0afa9b20 100644
--- a/Source/Modules/PrefMgr_Extension.swift
+++ b/Source/Modules/PrefMgr_Extension.swift
@@ -23,6 +23,9 @@ public extension PrefMgr {
     if #unavailable(macOS 12) {
       showNotificationsWhenTogglingCapsLock = false
     }
+    if appleLanguages.isEmpty {
+      UserDefaults.standard.removeObject(forKey: UserDef.kAppleLanguages.rawValue)
+    }
     // 自動糾正選字鍵 (利用其 didSet 特性)
     candidateKeys = candidateKeys
     // 客體黑名單資料類型升級。