-'error.activity_exists' => 'この名前の活動内容は既に存在します',
-// TODO: translate error.client_exists.
-// 'error.client_exists' => 'client with this name already exists',
+// TODO: translate the following.
+// 'error.task_exists' => 'Task with this name already exists.',
+// 'error.client_exists' => 'Client with this name already exists.',
+// 'error.invoice_exists' => 'Invoice with this number already exists.',
+// 'error.no_invoiceable_items' => 'There are no invoiceable items.',