Refactor and translate comments and docstrings in utility modules to English for better clarity and maintainability. Update Gunicorn and application startup messages for consistency in language. Enhance documentation with English translations for better accessibility.

backend_api_python/app/routes/billing.py

@@ -1,9 +1,9 @@
 """
-Billing APIs - 会员购买/套餐配置（Mock支付）
+Billing APIs - Membership purchase/package configuration (Mock payment)
 
-当前版本先实现“快速商业闭环”的最小可用：
-- 从系统设置(.env)读取 3 档会员（包月/包年/永久）金额与赠送积分配置
-- 用户在前端购买后立即开通/发放积分（后续可替换为真实支付网关）
+The current version first implements the minimum availability of "fast commercial closed loop":
+- Read the three levels of membership (monthly/annual/permanent) amounts and bonus points configuration from the system settings (.env)
+- Users activate/issue points immediately after purchasing on the front end (can be replaced with a real payment gateway later)
 """
 
 from flask import Blueprint, jsonify, request, g
@@ -59,7 +59,7 @@ def purchase_membership():
 
 
 # =========================
-# USDT Pay (方案B)
+# USDT Pay (Plan B)
 # =========================