diff --git a/apps/readest-app/src/app/reader/components/tts/TTSControl.tsx b/apps/readest-app/src/app/reader/components/tts/TTSControl.tsx
index 220c4985..5e0d0f17 100644
--- a/apps/readest-app/src/app/reader/components/tts/TTSControl.tsx
+++ b/apps/readest-app/src/app/reader/components/tts/TTSControl.tsx
@@ -99,7 +99,7 @@ const TTSControl = () => {
     const view = getView(bookKey);
     const viewSettings = getViewSettings(bookKey);
     const bookData = getBookData(bookKey);
-    if (!view || !viewSettings || !bookData) return;
+    if (!view || !viewSettings || !bookData || !bookData.book) return;
     if (bookData.book?.format === 'PDF') {
       eventDispatcher.dispatch('toast', {
         message: _('TTS not supported for PDF'),
@@ -108,6 +108,7 @@ const TTSControl = () => {
       return;
     }
 
+    const primaryLang = bookData.book.primaryLanguage;
     setBookKey(bookKey);
 
     if (ttsControllerRef.current) {
@@ -128,9 +129,13 @@ const TTSControl = () => {
       await ttsController.initViewTTS();
       const ssml = view.tts?.from(range);
       if (ssml) {
-        const lang = parseSSMLLang(ssml) || 'en';
-        setTtsLang(lang);
+        let lang = parseSSMLLang(ssml) || 'en';
+        // We will not trust 'en' language from ssml, as it may be a fallback or hardcoded value
+        if (lang === 'en' && primaryLang && primaryLang !== 'en') {
+          lang = primaryLang.split('-')[0]!;
+        }
         setIsPlaying(true);
+        setTtsLang(lang);
 
         ttsController.setLang(lang);
         ttsController.setRate(viewSettings.ttsRate);
diff --git a/apps/readest-app/src/services/appService.ts b/apps/readest-app/src/services/appService.ts
index 2d0ad613..ab1d8b96 100644
--- a/apps/readest-app/src/services/appService.ts
+++ b/apps/readest-app/src/services/appService.ts
@@ -15,6 +15,7 @@ import {
   formatTitle,
   formatAuthors,
   getFilename,
+  getPrimaryLanguage,
 } from '@/utils/book';
 import { partialMD5 } from '@/utils/md5';
 import { BookDoc, DocumentLoader } from '@/libs/document';
@@ -198,6 +199,7 @@ export abstract class BaseAppService implements AppService {
         format,
         title: formatTitle(loadedBook.metadata.title),
         author: formatAuthors(loadedBook.metadata.author, loadedBook.metadata.language),
+        primaryLanguage: getPrimaryLanguage(loadedBook.metadata.language),
         createdAt: existingBook ? existingBook.createdAt : Date.now(),
         uploadedAt: existingBook ? existingBook.uploadedAt : null,
         deletedAt: transient ? Date.now() : null,
@@ -208,6 +210,7 @@ export abstract class BaseAppService implements AppService {
       if (existingBook) {
         existingBook.title = book.title;
         existingBook.author = book.author;
+        existingBook.primaryLanguage = existingBook.primaryLanguage ?? book.primaryLanguage;
       }
 
       if (!(await this.fs.exists(getDir(book), 'Books'))) {
diff --git a/apps/readest-app/src/services/constants.ts b/apps/readest-app/src/services/constants.ts
index 4401a273..13ea1874 100644
--- a/apps/readest-app/src/services/constants.ts
+++ b/apps/readest-app/src/services/constants.ts
@@ -588,3 +588,5 @@ export const TRANSLATED_LANGS = {
   'zh-CN': '简体中文',
   'zh-TW': '正體中文',
 };
+
+export const SUPPORTED_LANGS: Record<string, string> = { ...TRANSLATED_LANGS, zh: '中文' };
diff --git a/apps/readest-app/src/services/tts/EdgeTTSClient.ts b/apps/readest-app/src/services/tts/EdgeTTSClient.ts
index 1804290c..501c53e7 100644
--- a/apps/readest-app/src/services/tts/EdgeTTSClient.ts
+++ b/apps/readest-app/src/services/tts/EdgeTTSClient.ts
@@ -6,6 +6,7 @@ import { TTSGranularity } from '@/types/view';
 import { TTSUtils } from './TTSUtils';
 
 export class EdgeTTSClient implements TTSClient {
+  #primaryLang = 'en';
   #rate = 1.0;
   #pitch = 1.0;
   #voice: TTSVoice | null = null;
@@ -50,7 +51,10 @@ export class EdgeTTSClient implements TTSClient {
     preload = false,
   ): AsyncGenerator<TTSMessageEvent> {
     const { marks } = parseSSMLMarks(ssml);
-    const lang = parseSSMLLang(ssml) || 'en';
+    let lang = parseSSMLLang(ssml) || 'en';
+    if (lang === 'en' && this.#primaryLang && this.#primaryLang !== 'en') {
+      lang = this.#primaryLang;
+    }
     let voiceId = 'en-US-AriaNeural';
     if (!this.#voice || this.#currentVoiceLang !== lang) {
       const preferredVoiceId = TTSUtils.getPreferredVoice('edge-tts', lang);
@@ -207,6 +211,10 @@ export class EdgeTTSClient implements TTSClient {
     }
   }
 
+  setPrimaryLang(lang: string) {
+    this.#primaryLang = lang;
+  }
+
   async setRate(rate: number) {
     // The Edge TTS API uses rate in [0.5 .. 2.0].
     this.#rate = rate;
diff --git a/apps/readest-app/src/services/tts/TTSClient.ts b/apps/readest-app/src/services/tts/TTSClient.ts
index 92906c36..12aa95f2 100644
--- a/apps/readest-app/src/services/tts/TTSClient.ts
+++ b/apps/readest-app/src/services/tts/TTSClient.ts
@@ -21,6 +21,7 @@ export interface TTSClient {
   pause(): Promise<void>;
   resume(): Promise<void>;
   stop(): Promise<void>;
+  setPrimaryLang(lang: string): void;
   setRate(rate: number): Promise<void>;
   setPitch(pitch: number): Promise<void>;
   setVoice(voice: string): Promise<void>;
diff --git a/apps/readest-app/src/services/tts/TTSController.ts b/apps/readest-app/src/services/tts/TTSController.ts
index 09a4cf3a..2f6e33c7 100644
--- a/apps/readest-app/src/services/tts/TTSController.ts
+++ b/apps/readest-app/src/services/tts/TTSController.ts
@@ -219,6 +219,12 @@ export class TTSController extends EventTarget {
 
   async setLang(lang: string) {
     this.ttsLang = lang;
+    this.setPrimaryLang(lang);
+  }
+
+  async setPrimaryLang(lang: string) {
+    this.ttsEdgeClient.setPrimaryLang(lang);
+    this.ttsWebClient.setPrimaryLang(lang);
   }
 
   async setRate(rate: number) {
diff --git a/apps/readest-app/src/services/tts/WebSpeechClient.ts b/apps/readest-app/src/services/tts/WebSpeechClient.ts
index 89957436..92ee07fd 100644
--- a/apps/readest-app/src/services/tts/WebSpeechClient.ts
+++ b/apps/readest-app/src/services/tts/WebSpeechClient.ts
@@ -173,6 +173,7 @@ async function* speakWithMarks(
 }
 
 export class WebSpeechClient implements TTSClient {
+  #primaryLang = 'en';
   #rate = 1.0;
   #pitch = 1.0;
   #voice: SpeechSynthesisVoice | null = null;
@@ -215,7 +216,10 @@ export class WebSpeechClient implements TTSClient {
     // no need to preload for web speech
     if (preload) return;
 
-    const lang = parseSSMLLang(ssml) || 'en';
+    let lang = parseSSMLLang(ssml) || 'en';
+    if (lang === 'en' && this.#primaryLang && this.#primaryLang !== 'en') {
+      lang = this.#primaryLang;
+    }
     if (!this.#voice || this.#currentVoiceLang !== lang) {
       const preferredVoiceId = TTSUtils.getPreferredVoice('web-speech', lang);
       const preferredVoice = this.#voices.find((v) => v.voiceURI === preferredVoiceId);
@@ -262,6 +266,10 @@ export class WebSpeechClient implements TTSClient {
     this.#synth.cancel();
   }
 
+  setPrimaryLang(lang: string) {
+    this.#primaryLang = lang;
+  }
+
   async setRate(rate: number) {
     // The Web Speech API uses utterance.rate in [0.1 .. 10],
     this.#rate = rate;
diff --git a/apps/readest-app/src/store/readerStore.ts b/apps/readest-app/src/store/readerStore.ts
index f19f7422..0f74629d 100644
--- a/apps/readest-app/src/store/readerStore.ts
+++ b/apps/readest-app/src/store/readerStore.ts
@@ -8,6 +8,7 @@ import { updateTocCFI, updateTocID } from '@/utils/toc';
 import { useSettingsStore } from './settingsStore';
 import { useBookDataStore } from './bookDataStore';
 import { useLibraryStore } from './libraryStore';
+import { getPrimaryLanguage } from '@/utils/book';
 
 interface ViewState {
   /* Unique key for each book view */
@@ -136,6 +137,9 @@ export const useReaderStore = create<ReaderStore>((set, get) => ({
           }, {});
           updateTocCFI(bookDoc, bookDoc.toc, sections);
         }
+        // Set the book's language for formerly imported books, newly imported books have this field set
+        book.primaryLanguage =
+          book.primaryLanguage ?? getPrimaryLanguage(bookDoc.metadata.language);
         useBookDataStore.setState((state) => ({
           booksData: {
             ...state.booksData,
diff --git a/apps/readest-app/src/types/book.ts b/apps/readest-app/src/types/book.ts
index 9b214aa9..d616fbd8 100644
--- a/apps/readest-app/src/types/book.ts
+++ b/apps/readest-app/src/types/book.ts
@@ -27,6 +27,7 @@ export interface Book {
 
   lastUpdated?: number; // deprecated in favor of updatedAt
   progress?: [number, number]; // Add progress field: [current, total], 1-based page number
+  primaryLanguage?: string;
 }
 
 export interface BookGroupType {
diff --git a/apps/readest-app/src/utils/book.ts b/apps/readest-app/src/utils/book.ts
index bbebe667..1b6ddb70 100644
--- a/apps/readest-app/src/utils/book.ts
+++ b/apps/readest-app/src/utils/book.ts
@@ -3,6 +3,7 @@ import { Book, BookConfig, BookProgress, WritingMode } from '@/types/book';
 import { getUserLang, isContentURI, isValidURL, makeSafeFilename } from './misc';
 import { getStorageType } from './object';
 import { getDirFromLanguage } from './rtl';
+import { SUPPORTED_LANGS } from '@/services/constants';
 
 export const getDir = (book: Book) => {
   return `${book.hash}`;
@@ -107,11 +108,17 @@ export const formatPublisher = (publisher: string | LanguageMap) => {
   return typeof publisher === 'string' ? publisher : formatLanguageMap(publisher);
 };
 
-export const formatLanguage = (lang: string | string[] | undefined) => {
-  return Array.isArray(lang) ? lang.join(', ') : lang;
+const langCodeToLangName = (langCode: string) => {
+  return SUPPORTED_LANGS[langCode] || langCode.toUpperCase();
 };
 
-export const primaryLanguage = (lang: string | string[] | undefined) => {
+export const formatLanguage = (lang: string | string[] | undefined): string => {
+  return Array.isArray(lang)
+    ? lang.map(langCodeToLangName).join(', ')
+    : langCodeToLangName(lang || '');
+};
+
+export const getPrimaryLanguage = (lang: string | string[] | undefined) => {
   return Array.isArray(lang) ? lang[0] : lang;
 };
 
@@ -159,6 +166,6 @@ export const getBookDirFromWritingMode = (writingMode: WritingMode) => {
 };
 
 export const getBookDirFromLanguage = (language: string | string[] | undefined) => {
-  const lang = primaryLanguage(language) || '';
+  const lang = getPrimaryLanguage(language) || '';
   return getDirFromLanguage(lang);
 };