feat: toggleable feature flags (#209)

locales/zh-CN.json

@@ -11,7 +11,8 @@
     "profile": "个人资料"
   },
   "nav_footer": {
-    "select_language": "选择语言"
+    "select_language": "选择语言",
+    "select_feature_flags": "切换功能标志"
   },
   "timeline": "时间轴",
   "title": {
@@ -22,5 +23,8 @@
     "followers": "被 {0} 人关注",
     "following": "正在关注 {0} 人",
     "posts": "{0} 条帖文"
+  },
+  "feature_flag": {
+    "virtual_scroll": "虚拟滚动"
   }
 }