add nlu fallback handling

config.yml

@@ -11,4 +11,6 @@ pipeline:
 # Configuration for Rasa Core.
 # https://rasa.com/docs/rasa/core/policies/
 policies:
-- name: RulePolicy
+- name: RulePolicy
+- name: FallbackClassifier
+  threshold: 0.7

data/rules.yml

@@ -16,3 +16,8 @@ rules:
   steps:
   - intent: out_of_scope
   - action: action_human_handoff
+
+- rule: Ask the user to rephrase whenever they send a message with low NLU confidence
+  steps:
+  - intent: nlu_fallback
+  - action: utter_please_rephrase

domain.yml

@@ -9,7 +9,10 @@ actions:
   - action_ReversePhoneLookup
   - action_CallReservationHotline
   - action_human_handoff
-   
+
+responses:
+  utter_please_rephrase:
+  - text: 不好意思，我不太明白您的意思。可以請您再說一次嗎？ 
 
 session_config:
   session_expiration_time: 60