Update translations.json

server/translations.json

@@ -468,7 +468,7 @@
     "white-out": "修正液",
     "zoom": "放大"
   },
-    "zh_tw": {
+    "zh-tw": {
     "board_name_placeholder": "白板名稱",
     "circle": "圓形",
     "click_to_toggle": "點擊以切換",