diff --git a/public/locales/ko/translation.json b/public/locales/ko/translation.json
index fcfb6b4..7a6aa85 100644
--- a/public/locales/ko/translation.json
+++ b/public/locales/ko/translation.json
@@ -7,8 +7,8 @@
   "chat-edit-cancel": "취소",
   "chat-edit-content": "내용",
   "chat-edit-delete": "삭제",
-  "chat-edit-insert-after": "",
-  "chat-edit-insert-before": "",
+  "chat-edit-insert-after": "이 메시지 뒤에 삽입",
+  "chat-edit-insert-before": "이 메시지 앞에 삽입",
   "chat-edit-is-breaking": "이 다음 메시지부터 스크린샷 나누기",
   "chat-edit-name-override": "이름 바꿔쓰기",
   "chat-edit-sender": "발신자",
@@ -58,7 +58,7 @@
   "topbar-show-help": "도움말",
   "topbar-show-info": "개요",
   "topbar-show-menu": "메뉴",
-  "yuzu-background-avatar": "",
+  "yuzu-background-avatar": "아바타 배경",
   "yuzu-kizuna-text": "{}의 인연 스토리로",
   "yuzu-kizuna-title": "인연 이벤트",
   "yuzu-reply-title": "답장하기",
diff --git a/public/locales/zh-TW/translation.json b/public/locales/zh-TW/translation.json
index 92e7a5f..63b76ea 100644
--- a/public/locales/zh-TW/translation.json
+++ b/public/locales/zh-TW/translation.json
@@ -1,67 +1,67 @@
 {
-  "app-cfg-width": "",
-  "app-cfg-width-100vw": "",
-  "app-cfg-width-80vw": "",
-  "chat-edit-always-show-avatar": "",
-  "chat-edit-apply": "",
-  "chat-edit-cancel": "",
-  "chat-edit-content": "",
-  "chat-edit-delete": "",
-  "chat-edit-insert-after": "",
-  "chat-edit-insert-before": "",
-  "chat-edit-is-breaking": "",
-  "chat-edit-name-override": "",
-  "chat-edit-sender": "",
-  "chat-input-placeholder": "",
-  "clear-chat-confirm-cancel": "",
-  "clear-chat-confirm-text": "",
-  "clear-chat-confirm-title": "",
-  "clear-chat-confirm-yes": "",
-  "common-cfg-width": "",
-  "custom-char-create": "",
-  "custom-char-name": "",
-  "custom-char-title": "",
-  "data-version": "",
-  "item-type": "",
-  "item-type-choices": "",
-  "item-type-image": "",
-  "item-type-narration": "",
-  "item-type-relationship-story": "",
-  "item-type-section-title": "",
-  "item-type-selection": "",
-  "item-type-text": "",
-  "item-type-thoughts": "",
-  "latest-update": "",
-  "previous-updates": "",
-  "remove-custom-char-confirm-cancel": "",
-  "remove-custom-char-confirm-text": "",
-  "remove-custom-char-confirm-title": "",
-  "remove-custom-char-confirm-yes": "",
-  "save-code-dialog-cancel": "",
-  "save-code-dialog-no-save-custom-chars": "",
-  "save-code-dialog-save": "",
-  "save-code-dialog-save-active-chars": "",
-  "save-code-dialog-save-active-custom-chars": "",
-  "save-code-dialog-save-all-custom-chars": "",
-  "save-code-dialog-save-chat": "",
-  "save-code-dialog-save-used-custom-chars": "",
-  "save-code-dialog-title": "",
-  "search-label": "",
-  "source-enabled": "",
-  "topbar-clear-chat": "",
-  "topbar-config": "",
-  "topbar-feedback": "",
-  "topbar-load-code": "",
-  "topbar-save-code": "",
-  "topbar-save-image": "",
-  "topbar-show-charlist": "",
-  "topbar-show-help": "",
-  "topbar-show-info": "",
-  "topbar-show-menu": "",
-  "yuzu-background-avatar": "",
+  "app-cfg-width": "頁面寬度",
+  "app-cfg-width-100vw": "100% 視窗",
+  "app-cfg-width-80vw": "80% 視窗",
+  "chat-edit-always-show-avatar": "顯示頭像",
+  "chat-edit-apply": "確認",
+  "chat-edit-cancel": "取消",
+  "chat-edit-content": "內容",
+  "chat-edit-delete": "刪除",
+  "chat-edit-insert-after": "在此訊息之後插入",
+  "chat-edit-insert-before": "在此訊息之前插入",
+  "chat-edit-is-breaking": "截圖時在這裡分割圖片",
+  "chat-edit-name-override": "臨時改名",
+  "chat-edit-sender": "發送自",
+  "chat-input-placeholder": "聊天內容",
+  "clear-chat-confirm-cancel": "取消",
+  "clear-chat-confirm-text": "未儲存的聊天內容將無法找回！",
+  "clear-chat-confirm-title": "清空全部聊天？",
+  "clear-chat-confirm-yes": "清空",
+  "common-cfg-width": "聊天框寬度",
+  "custom-char-create": "上傳頭像",
+  "custom-char-name": "名字",
+  "custom-char-title": "建立自訂角色",
+  "data-version": "資料版本",
+  "item-type": "類型",
+  "item-type-choices": "選項",
+  "item-type-image": "圖片",
+  "item-type-narration": "旁白",
+  "item-type-relationship-story": "羈絆事件",
+  "item-type-section-title": "小標題",
+  "item-type-selection": "選擇",
+  "item-type-text": "文字",
+  "item-type-thoughts": "內心獨白",
+  "latest-update": "最近更新",
+  "previous-updates": "更新歷史",
+  "remove-custom-char-confirm-cancel": "取消",
+  "remove-custom-char-confirm-text": "如果刪除了角色，TA 的對話會在刷新後變成玩家說的話",
+  "remove-custom-char-confirm-title": "要刪除這個角色嗎？",
+  "remove-custom-char-confirm-yes": "刪除",
+  "save-code-dialog-cancel": "取消",
+  "save-code-dialog-no-save-custom-chars": "不儲存自訂角色",
+  "save-code-dialog-save": "下載",
+  "save-code-dialog-save-active-chars": "儲存右下角角色清單",
+  "save-code-dialog-save-active-custom-chars": "儲存右下角出現的自訂角色",
+  "save-code-dialog-save-all-custom-chars": "儲存所有自訂角色",
+  "save-code-dialog-save-chat": "儲存對話",
+  "save-code-dialog-save-used-custom-chars": "儲存對話中出現的自訂角色",
+  "save-code-dialog-title": "下載對話資料 JSON 檔案",
+  "search-label": "搜尋",
+  "source-enabled": "包含這些角色",
+  "topbar-clear-chat": "清空聊天",
+  "topbar-config": "渲染設定",
+  "topbar-feedback": "回饋",
+  "topbar-load-code": "匯入代碼",
+  "topbar-save-code": "儲存代碼",
+  "topbar-save-image": "儲存圖片",
+  "topbar-show-charlist": "角色",
+  "topbar-show-help": "幫助",
+  "topbar-show-info": "關於",
+  "topbar-show-menu": "選單",
+  "yuzu-background-avatar": "頭像背景",
   "yuzu-kizuna-text": "前往{}的羈絆劇情。",
   "yuzu-kizuna-title": "羈絆活動",
   "yuzu-reply-title": "回覆",
-  "yuzu-sensei": "",
-  "yuzu-theme": ""
+  "yuzu-sensei": "老師",
+  "yuzu-theme": "配色"
 }
diff --git a/src/App.tsx b/src/App.tsx
index f6cfd1e..58f4218 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -2,6 +2,7 @@ import { Box } from "@mui/system";
 import { useEffect, useState } from "react";
 import { useMediaQuery } from "react-responsive";
 import "./App.css";
+import { getInitialLanguage } from "./i18n";
 import AppConfig, { loadAppConfig, saveAppConfig } from "./model/AppConfig";
 import { AppContext } from "./model/AppContext";
 import AppData from "./model/AppData";
@@ -22,7 +23,7 @@ import TopBar from "./view/TopBar";
 function App() {
   const [loaded, setLoaded] = useState(false);
   const [renderer, setRenderer] = useState((localStorage.getItem("renderer") || Renderers[1]) as RendererType);
-  const [lang, setLang] = useState(localStorage.getItem("lang") || "zh-cn");
+  const [lang, setLang] = useState(() => getInitialLanguage());
   const [activeChars, setActiveChars] = useState<ChatChar[]>([]);
   const [characters, setCharacters] = useState(new Map<string, Character>());
   const [stamps, setStamps] = useState<StampInfo[][]>([]);
diff --git a/src/i18n.ts b/src/i18n.ts
index c799d5e..bb4c7a8 100644
--- a/src/i18n.ts
+++ b/src/i18n.ts
@@ -2,11 +2,52 @@ import i18n from "i18next";
 import { initReactI18next } from "react-i18next";
 import Backend from "i18next-http-backend";
 
+const supportedLanguages = new Set(["en", "ja", "ko", "zh-cn", "zh-tw"]);
+
+const normalizeLanguage = (lang: string) => {
+  const lower = lang.toLowerCase();
+  if (lower.startsWith("zh")) {
+    if (lower.includes("tw") || lower.includes("hant") || lower.includes("hk") || lower.includes("mo")) {
+      return "zh-tw";
+    }
+    return "zh-cn";
+  }
+  if (lower.startsWith("en")) {
+    return "en";
+  }
+  if (lower.startsWith("ja")) {
+    return "ja";
+  }
+  if (lower.startsWith("ko")) {
+    return "ko";
+  }
+  return null;
+};
+
+const getBrowserLanguage = () => {
+  if (typeof navigator === "undefined") {
+    return null;
+  }
+  const candidates = [...(navigator.languages || []), navigator.language].filter(Boolean);
+
+  return candidates.map(normalizeLanguage).find(lang => lang && supportedLanguages.has(lang)) ?? null;
+};
+
+export const getInitialLanguage = () => {
+  const stored = localStorage.getItem("lang");
+  if (stored) {
+    return stored;
+  }
+  const initial = getBrowserLanguage() || "zh-cn";
+  localStorage.setItem("lang", initial);
+  return initial;
+};
+
 i18n
   .use(Backend)
   .use(initReactI18next)
   .init({
-    lng: localStorage.getItem("lang") || "zh-cn",
+    lng: getInitialLanguage(),
     fallbackLng: "en",
     interpolation: {
       escapeValue: false,