refactor(i18n): 扁平化所有国际化语言文件的翻译结构

移除多层嵌套的翻译对象，将所有翻译项直接挂载到顶层lang对象上，统一代码结构

lang/en-us/member/public.js

@@ -1,11 +1,7 @@
 export const lang = {
 	// member/public member common mixin
-	member: {
-		public: {
-			// Risk warning
-			riskWarningTitle: 'Risk Warning',
-			// Confirm account cancellation
-			cancelAccountConfirm: 'Are you sure you want to cancel the current account?',
-		},
-	},
+	// Risk warning
+	riskWarningTitle: 'Risk Warning',
+	// Confirm account cancellation
+	cancelAccountConfirm: 'Are you sure you want to cancel the current account?',
 }