diff --git a/app/api/generate/scene-content/route.ts b/app/api/generate/scene-content/route.ts
index db9b772e..4ff71229 100644
--- a/app/api/generate/scene-content/route.ts
+++ b/app/api/generate/scene-content/route.ts
@@ -13,6 +13,7 @@ import {
   generateSceneContent,
   buildVisionUserContent,
 } from '@/lib/generation/generation-pipeline';
+import { normalizeGenerationLanguage } from '@/lib/generation/language';
 import type { AgentInfo } from '@/lib/generation/generation-pipeline';
 import type { SceneOutline, PdfImage, ImageMapping } from '@/lib/types/generation';
 import { createLogger } from '@/lib/logger';
@@ -67,7 +68,7 @@ export async function POST(req: NextRequest) {
     // Ensure outline has language from stageInfo (fallback for older outlines)
     const outline: SceneOutline = {
       ...rawOutline,
-      language: rawOutline.language || (stageInfo?.language as 'zh-CN' | 'en-US') || 'zh-CN',
+      language: rawOutline.language ?? normalizeGenerationLanguage(stageInfo?.language),
     };
 
     // ── Model resolution from request headers ──
diff --git a/lib/generation/language.ts b/lib/generation/language.ts
new file mode 100644
index 00000000..b1a8ab9a
--- /dev/null
+++ b/lib/generation/language.ts
@@ -0,0 +1,112 @@
+export type SupportedGenerationLanguage = 'zh-CN' | 'en-US' | 'ru-RU';
+
+export interface GenerationLanguageSpec {
+  code: SupportedGenerationLanguage;
+  englishName: string;
+  nativeName: string;
+  noImagesAvailableText: string;
+  noneText: string;
+  noImagesForSlideText: string;
+  autoGenerateElementsText: string;
+  slideFocusTitle: string;
+  slideSpeechTitle: string;
+  slideSpeechFallback: string;
+  quizGuideTitle: string;
+  quizGuideText: string;
+  interactiveGuideTitle: string;
+  interactiveGuideText: string;
+  pblIntroTitle: string;
+  pblIntroText: string;
+}
+
+const SPECS: Record<SupportedGenerationLanguage, GenerationLanguageSpec> = {
+  'zh-CN': {
+    code: 'zh-CN',
+    englishName: 'Chinese',
+    nativeName: '中文',
+    noImagesAvailableText: '无可用图片',
+    noneText: '无',
+    noImagesForSlideText: '无可用图片，禁止插入任何 image 元素',
+    autoGenerateElementsText: '（根据要点自动生成）',
+    slideFocusTitle: '聚焦重点',
+    slideSpeechTitle: '场景讲解',
+    slideSpeechFallback: '请先关注这一页的核心要点。',
+    quizGuideTitle: '测验引导',
+    quizGuideText: '现在让我们来做一个小测验，检验一下学习成果。',
+    interactiveGuideTitle: '交互引导',
+    interactiveGuideText:
+      '现在让我们通过交互式可视化来探索这个概念。请尝试操作页面中的元素，观察变化。',
+    pblIntroTitle: 'PBL 项目介绍',
+    pblIntroText:
+      '现在让我们开始一个项目式学习活动。请选择你的角色，查看任务看板，开始协作完成项目。',
+  },
+  'en-US': {
+    code: 'en-US',
+    englishName: 'English',
+    nativeName: 'English',
+    noImagesAvailableText: 'No images available',
+    noneText: 'None',
+    noImagesForSlideText: 'No images available. Do not insert any image elements.',
+    autoGenerateElementsText: '(generate automatically from the key points)',
+    slideFocusTitle: 'Focus on the key point',
+    slideSpeechTitle: 'Scene explanation',
+    slideSpeechFallback: "Let's focus on the key ideas on this page first.",
+    quizGuideTitle: 'Quiz guidance',
+    quizGuideText: "Let's do a short quiz now to check what we have learned.",
+    interactiveGuideTitle: 'Interactive guidance',
+    interactiveGuideText:
+      "Now let's explore this concept through an interactive visualization. Try the controls on the page and observe what changes.",
+    pblIntroTitle: 'PBL project introduction',
+    pblIntroText:
+      "Now let's begin a project-based learning activity. Choose your role, review the task board, and start collaborating on the project.",
+  },
+  'ru-RU': {
+    code: 'ru-RU',
+    englishName: 'Russian',
+    nativeName: 'Русский',
+    noImagesAvailableText: 'Нет доступных изображений',
+    noneText: 'Нет',
+    noImagesForSlideText: 'Нет доступных изображений. Не вставляй элементы image.',
+    autoGenerateElementsText: 'сгенерируй автоматически по ключевым пунктам',
+    slideFocusTitle: 'Фокус на главном',
+    slideSpeechTitle: 'Объяснение сцены',
+    slideSpeechFallback: 'Сначала разберём ключевые идеи этой страницы.',
+    quizGuideTitle: 'Введение к квизу',
+    quizGuideText: 'Сейчас сделаем короткий квиз, чтобы проверить, что уже усвоили.',
+    interactiveGuideTitle: 'Введение к интерактиву',
+    interactiveGuideText:
+      'Теперь давай разберём этот концепт через интерактивную визуализацию. Попробуй элементы управления на странице и посмотри, что меняется.',
+    pblIntroTitle: 'Введение в PBL-проект',
+    pblIntroText:
+      'Теперь начинаем проектное задание. Выбери роль, посмотри на доску задач и приступай к совместной работе над проектом.',
+  },
+};
+
+export function normalizeGenerationLanguage(language?: string): SupportedGenerationLanguage {
+  const normalized = (language || '').trim().toLowerCase();
+
+  if (normalized.startsWith('ru')) return 'ru-RU';
+  if (normalized.startsWith('en')) return 'en-US';
+  if (normalized.startsWith('zh')) return 'zh-CN';
+
+  return 'zh-CN';
+}
+
+export function getGenerationLanguageSpec(language?: string): GenerationLanguageSpec {
+  return SPECS[normalizeGenerationLanguage(language)];
+}
+
+export function buildLanguageInstruction(language?: string): string {
+  const spec = getGenerationLanguageSpec(language);
+
+  return [
+    `Output language must be ${spec.englishName} (${spec.nativeName}).`,
+    `All natural-language text, titles, explanations, quiz text, hints, labels, and UI copy must be in ${spec.englishName}.`,
+    spec.code === 'ru-RU'
+      ? 'English is allowed only for code, SQL keywords, API field names, or other technical syntax that must remain unchanged.'
+      : 'Keep technical syntax unchanged only when necessary.',
+    spec.code === 'ru-RU'
+      ? 'Never output Chinese.'
+      : 'Do not switch to another language unless the user explicitly asks for it.',
+  ].join(' ');
+}
diff --git a/lib/generation/outline-generator.ts b/lib/generation/outline-generator.ts
index 4849bcef..97a46179 100644
--- a/lib/generation/outline-generator.ts
+++ b/lib/generation/outline-generator.ts
@@ -12,6 +12,7 @@ import type {
   ImageMapping,
 } from '@/lib/types/generation';
 import { buildPrompt, PROMPT_IDS } from './prompts';
+import { getGenerationLanguageSpec } from './language';
 import { formatImageDescription, formatImagePlaceholder } from './prompt-formatters';
 import { parseJsonResponse } from './json-repair';
 import { uniquifyMediaElementIds } from './scene-builder';
@@ -38,9 +39,10 @@ export async function generateSceneOutlinesFromRequirements(
     teacherContext?: string;
   },
 ): Promise<GenerationResult<SceneOutline[]>> {
+  const languageSpec = getGenerationLanguageSpec(requirements.language);
+
   // Build available images description for the prompt
-  let availableImagesText =
-    requirements.language === 'zh-CN' ? '无可用图片' : 'No images available';
+  let availableImagesText = languageSpec.noImagesAvailableText;
   let visionImages: Array<{ id: string; src: string }> | undefined;
 
   if (pdfImages && pdfImages.length > 0) {
@@ -99,16 +101,11 @@ export async function generateSceneOutlinesFromRequirements(
     // New simplified variables
     requirement: requirements.requirement,
     language: requirements.language,
-    pdfContent: pdfText
-      ? pdfText.substring(0, MAX_PDF_CONTENT_CHARS)
-      : requirements.language === 'zh-CN'
-        ? '无'
-        : 'None',
+    pdfContent: pdfText ? pdfText.substring(0, MAX_PDF_CONTENT_CHARS) : languageSpec.noneText,
     availableImages: availableImagesText,
     userProfile: userProfileText,
     mediaGenerationPolicy,
-    researchContext:
-      options?.researchContext || (requirements.language === 'zh-CN' ? '无' : 'None'),
+    researchContext: options?.researchContext || languageSpec.noneText,
     // Server-side generation populates this via options; client-side populates via formatTeacherPersonaForPrompt
     teacherContext: options?.teacherContext || '',
   });
diff --git a/lib/generation/prompt-formatters.ts b/lib/generation/prompt-formatters.ts
index 4486ba09..12732ad9 100644
--- a/lib/generation/prompt-formatters.ts
+++ b/lib/generation/prompt-formatters.ts
@@ -3,6 +3,7 @@
  */
 
 import type { PdfImage } from '@/lib/types/generation';
+import { getGenerationLanguageSpec } from './language';
 import type { AgentInfo, SceneGenerationContext } from './pipeline-types';
 
 /** Build a course context string for injection into action prompts */
@@ -76,15 +77,23 @@ export function formatTeacherPersonaForPrompt(agents?: AgentInfo[]): string {
  * Includes dimension/aspect-ratio info when available.
  */
 export function formatImageDescription(img: PdfImage, language: string): string {
+  const spec = getGenerationLanguageSpec(language);
   let dimInfo = '';
   if (img.width && img.height) {
     const ratio = (img.width / img.height).toFixed(2);
-    dimInfo = ` | 尺寸: ${img.width}×${img.height} (宽高比${ratio})`;
+    dimInfo =
+      spec.code === 'zh-CN'
+        ? ` | 尺寸: ${img.width}×${img.height} (宽高比${ratio})`
+        : ` | dimensions: ${img.width}×${img.height} (aspect ratio ${ratio})`;
   }
   const desc = img.description ? ` | ${img.description}` : '';
-  return language === 'zh-CN'
-    ? `- **${img.id}**: 来自PDF第${img.pageNumber}页${dimInfo}${desc}`
-    : `- **${img.id}**: from PDF page ${img.pageNumber}${dimInfo}${desc}`;
+  if (spec.code === 'zh-CN') {
+    return `- **${img.id}**: 来自PDF第${img.pageNumber}页${dimInfo}${desc}`;
+  }
+  if (spec.code === 'ru-RU') {
+    return `- **${img.id}**: из PDF, страница ${img.pageNumber}${dimInfo}${desc}`;
+  }
+  return `- **${img.id}**: from PDF page ${img.pageNumber}${dimInfo}${desc}`;
 }
 
 /**
@@ -92,14 +101,22 @@ export function formatImageDescription(img: PdfImage, language: string): string
  * Only ID + page + dimensions + aspect ratio (no description), since the model can see the actual image.
  */
 export function formatImagePlaceholder(img: PdfImage, language: string): string {
+  const spec = getGenerationLanguageSpec(language);
   let dimInfo = '';
   if (img.width && img.height) {
     const ratio = (img.width / img.height).toFixed(2);
-    dimInfo = ` | 尺寸: ${img.width}×${img.height} (宽高比${ratio})`;
+    dimInfo =
+      spec.code === 'zh-CN'
+        ? ` | 尺寸: ${img.width}×${img.height} (宽高比${ratio})`
+        : ` | dimensions: ${img.width}×${img.height} (aspect ratio ${ratio})`;
+  }
+  if (spec.code === 'zh-CN') {
+    return `- **${img.id}**: PDF第${img.pageNumber}页的图片${dimInfo} [参见附图]`;
+  }
+  if (spec.code === 'ru-RU') {
+    return `- **${img.id}**: изображение со страницы ${img.pageNumber} PDF${dimInfo} [см. вложение]`;
   }
-  return language === 'zh-CN'
-    ? `- **${img.id}**: PDF第${img.pageNumber}页的图片${dimInfo} [参见附图]`
-    : `- **${img.id}**: image from PDF page ${img.pageNumber}${dimInfo} [see attached]`;
+  return `- **${img.id}**: image from PDF page ${img.pageNumber}${dimInfo} [see attached]`;
 }
 
 /**
@@ -121,7 +138,7 @@ export function buildVisionUserContent(
       let dimInfo = '';
       if (img.width && img.height) {
         const ratio = (img.width / img.height).toFixed(2);
-        dimInfo = ` (${img.width}×${img.height}, 宽高比${ratio})`;
+        dimInfo = ` (${img.width}×${img.height}, aspect ratio ${ratio})`;
       }
       parts.push({ type: 'text', text: `\n**${img.id}**${dimInfo}:` });
       // Strip data URI prefix — AI SDK only accepts http(s) URLs or raw base64
diff --git a/lib/generation/prompts/templates/requirements-to-outlines/user.md b/lib/generation/prompts/templates/requirements-to-outlines/user.md
index 65d0a492..263f0ae8 100644
--- a/lib/generation/prompts/templates/requirements-to-outlines/user.md
+++ b/lib/generation/prompts/templates/requirements-to-outlines/user.md
@@ -14,7 +14,7 @@ Please generate scene outlines based on the following course requirements.
 
 **Required language**: {{language}}
 
-(If language is zh-CN, all content must be in Chinese; if en-US, all content must be in English)
+All content must be in the required language above. Do not switch to another language.
 
 ---
 
diff --git a/lib/generation/scene-generator.ts b/lib/generation/scene-generator.ts
index 1dc22937..f857f9bb 100644
--- a/lib/generation/scene-generator.ts
+++ b/lib/generation/scene-generator.ts
@@ -23,6 +23,7 @@ import type { StageStore } from '@/lib/api/stage-api';
 import { createStageAPI } from '@/lib/api/stage-api';
 import { generatePBLContent } from '@/lib/pbl/generate-pbl';
 import { buildPrompt, PROMPT_IDS } from './prompts';
+import { getGenerationLanguageSpec } from './language';
 import { postProcessInteractiveHtml } from './interactive-post-processor';
 import { parseActionsFromStructuredOutput } from './action-parser';
 import { parseJsonResponse } from './json-repair';
@@ -468,9 +469,10 @@ async function generateSlideContent(
   agents?: AgentInfo[],
 ): Promise<GeneratedSlideContent | null> {
   const lang = outline.language || 'zh-CN';
+  const languageSpec = getGenerationLanguageSpec(lang);
 
   // Build assigned images description for the prompt
-  let assignedImagesText = '无可用图片，禁止插入任何 image 元素';
+  let assignedImagesText = languageSpec.noImagesForSlideText;
   let visionImages: Array<{ id: string; src: string }> | undefined;
 
   if (assignedImages && assignedImages.length > 0) {
@@ -539,7 +541,7 @@ async function generateSlideContent(
     title: outline.title,
     description: outline.description,
     keyPoints: (outline.keyPoints || []).map((p, i) => `${i + 1}. ${p}`).join('\n'),
-    elements: '（根据要点自动生成）',
+    elements: languageSpec.autoGenerateElementsText,
     assignedImages: assignedImagesText,
     canvas_width: canvasWidth,
     canvas_height: canvasHeight,
@@ -735,7 +737,7 @@ function normalizeQuizAnswer(question: Record<string, unknown>): string[] | unde
 async function generateInteractiveContent(
   outline: SceneOutline,
   aiCall: AICallFn,
-  language: 'zh-CN' | 'en-US' = 'zh-CN',
+  language: SceneOutline['language'] = 'zh-CN',
 ): Promise<GeneratedInteractiveContent | null> {
   const config = outline.interactiveConfig!;
 
@@ -1035,13 +1037,15 @@ export async function generateSceneActions(
 /**
  * Generate default PBL Actions (fallback)
  */
-function generateDefaultPBLActions(_outline: SceneOutline): Action[] {
+function generateDefaultPBLActions(outline: SceneOutline): Action[] {
+  const languageSpec = getGenerationLanguageSpec(outline.language);
+
   return [
     {
       id: `action_${nanoid(8)}`,
       type: 'speech',
-      title: 'PBL 项目介绍',
-      text: '现在让我们开始一个项目式学习活动。请选择你的角色，查看任务看板，开始协作完成项目。',
+      title: languageSpec.pblIntroTitle,
+      text: languageSpec.pblIntroText,
     },
   ];
 }
@@ -1140,6 +1144,7 @@ function processActions(actions: Action[], elements: PPTElement[], agents?: Agen
  * Generate default slide Actions (fallback)
  */
 function generateDefaultSlideActions(outline: SceneOutline, elements: PPTElement[]): Action[] {
+  const languageSpec = getGenerationLanguageSpec(outline.language);
   const actions: Action[] = [];
 
   // Add spotlight for text elements
@@ -1148,19 +1153,20 @@ function generateDefaultSlideActions(outline: SceneOutline, elements: PPTElement
     actions.push({
       id: `action_${nanoid(8)}`,
       type: 'spotlight',
-      title: '聚焦重点',
+      title: languageSpec.slideFocusTitle,
       elementId: textElements[0].id,
     });
   }
 
   // Add opening speech based on key points
+  const joiner = languageSpec.code === 'zh-CN' ? '。' : '. ';
   const speechText = outline.keyPoints?.length
-    ? outline.keyPoints.join('。') + '。'
-    : outline.description || outline.title;
+    ? `${outline.keyPoints.join(joiner)}${languageSpec.code === 'zh-CN' ? '。' : '.'}`
+    : outline.description || outline.title || languageSpec.slideSpeechFallback;
   actions.push({
     id: `action_${nanoid(8)}`,
     type: 'speech',
-    title: '场景讲解',
+    title: languageSpec.slideSpeechTitle,
     text: speechText,
   });
 
@@ -1170,13 +1176,15 @@ function generateDefaultSlideActions(outline: SceneOutline, elements: PPTElement
 /**
  * Generate default quiz Actions (fallback)
  */
-function generateDefaultQuizActions(_outline: SceneOutline): Action[] {
+function generateDefaultQuizActions(outline: SceneOutline): Action[] {
+  const languageSpec = getGenerationLanguageSpec(outline.language);
+
   return [
     {
       id: `action_${nanoid(8)}`,
       type: 'speech',
-      title: '测验引导',
-      text: '现在让我们来做一个小测验，检验一下学习成果。',
+      title: languageSpec.quizGuideTitle,
+      text: languageSpec.quizGuideText,
     },
   ];
 }
@@ -1184,13 +1192,15 @@ function generateDefaultQuizActions(_outline: SceneOutline): Action[] {
 /**
  * Generate default interactive Actions (fallback)
  */
-function generateDefaultInteractiveActions(_outline: SceneOutline): Action[] {
+function generateDefaultInteractiveActions(outline: SceneOutline): Action[] {
+  const languageSpec = getGenerationLanguageSpec(outline.language);
+
   return [
     {
       id: `action_${nanoid(8)}`,
       type: 'speech',
-      title: '交互引导',
-      text: '现在让我们通过交互式可视化来探索这个概念。请尝试操作页面中的元素，观察变化。',
+      title: languageSpec.interactiveGuideTitle,
+      text: languageSpec.interactiveGuideText,
     },
   ];
 }
diff --git a/lib/server/classroom-generation.ts b/lib/server/classroom-generation.ts
index eda67b4c..6d64a90c 100644
--- a/lib/server/classroom-generation.ts
+++ b/lib/server/classroom-generation.ts
@@ -26,6 +26,7 @@ import {
   replaceMediaPlaceholders,
   generateTTSForClassroom,
 } from '@/lib/server/classroom-media-generation';
+import { buildLanguageInstruction, normalizeGenerationLanguage } from '@/lib/generation/language';
 import type { UserRequirements } from '@/lib/types/generation';
 import type { Scene, Stage } from '@/lib/types/stage';
 
@@ -96,10 +97,6 @@ function createInMemoryStore(stage: Stage): StageStore {
   };
 }
 
-function normalizeLanguage(language?: string): 'zh-CN' | 'en-US' {
-  return language === 'en-US' ? 'en-US' : 'zh-CN';
-}
-
 function stripCodeFences(text: string): string {
   let cleaned = text.trim();
   if (cleaned.startsWith('```')) {
@@ -188,13 +185,19 @@ export async function generateClassroom(
     );
   }
 
+  const lang = normalizeGenerationLanguage(input.language);
+  const languageInstruction = buildLanguageInstruction(lang);
+
   const aiCall: AICallFn = async (systemPrompt, userPrompt, _images) => {
     const result = await callLLM(
       {
         model: languageModel,
         messages: [
-          { role: 'system', content: systemPrompt },
-          { role: 'user', content: userPrompt },
+          { role: 'system', content: `${languageInstruction}\n\n${systemPrompt}` },
+          {
+            role: 'user',
+            content: `${userPrompt}\n\nLanguage enforcement: ${languageInstruction}`,
+          },
         ],
         maxOutputTokens: modelInfo?.outputWindow,
       },
@@ -203,7 +206,6 @@ export async function generateClassroom(
     return result.text;
   };
 
-  const lang = normalizeLanguage(input.language);
   const requirements: UserRequirements = {
     requirement,
     language: lang,
diff --git a/lib/types/generation.ts b/lib/types/generation.ts
index c1e6eb7a..0162efc0 100644
--- a/lib/types/generation.ts
+++ b/lib/types/generation.ts
@@ -7,6 +7,7 @@
 
 import type { ActionType } from './action';
 import type { MediaGenerationRequest } from '@/lib/media/types';
+import type { SupportedGenerationLanguage } from '@/lib/generation/language';
 
 // ==================== PDF Image Types ====================
 
@@ -64,7 +65,7 @@ export interface UploadedDocument {
  */
 export interface UserRequirements {
   requirement: string; // Single free-form text for all user input
-  language: 'zh-CN' | 'en-US'; // Course language - critical for generation
+  language: SupportedGenerationLanguage; // Course language - critical for generation
   userNickname?: string; // Student nickname for personalization
   userBio?: string; // Student background for personalization
   webSearch?: boolean; // Enable web search for richer context
@@ -100,7 +101,7 @@ export interface SceneOutline {
   teachingObjective?: string;
   estimatedDuration?: number; // seconds
   order: number;
-  language?: 'zh-CN' | 'en-US'; // Generation language (inherited from requirements)
+  language?: SupportedGenerationLanguage; // Generation language (inherited from requirements)
   // Suggested image IDs (from PDF-extracted images)
   suggestedImageIds?: string[]; // e.g., ["img_1", "img_3"]
   // AI-generated media requests (when PDF images are insufficient)
@@ -124,7 +125,7 @@ export interface SceneOutline {
     projectDescription: string;
     targetSkills: string[];
     issueCount?: number;
-    language: 'zh-CN' | 'en-US';
+    language: SupportedGenerationLanguage;
   };
 }