diff --git a/Language/ja/Language.php b/Language/ja/Language.php
new file mode 100644
index 00000000..96bafecd
--- /dev/null
+++ b/Language/ja/Language.php
@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+// "Language" language settings
+return [
+    'invalidMessageFormat' => '不正なメッセージフォーマット: "{0}", 引数: "{1}"', // 'Invalid message format: "{0}", args: "{1}"'
+];