THU-MAIC · GRIZZZZZLY · Apr 17, 2026 · Apr 17, 2026
diff --git a/app/api/generate/scene-content/route.ts b/app/api/generate/scene-content/route.ts
@@ -33,7 +33,7 @@ export async function POST(req: NextRequest) {
       allOutlines,
       pdfImages,
       imageMapping,
-      stageInfo: _stageInfo,
+      stageInfo,
       stageId,
       agents,
       languageDirective,
@@ -45,6 +45,7 @@ export async function POST(req: NextRequest) {
       stageInfo: {
         name: string;
         description?: string;
+        language?: string;
         style?: string;
       };
       stageId: string;
@@ -67,7 +68,16 @@ export async function POST(req: NextRequest) {
       return apiError('MISSING_REQUIRED_FIELD', 400, 'stageId is required');
     }
 
-    const outline: SceneOutline = { ...rawOutline };
+    const outline: SceneOutline = {
+      ...rawOutline,
+      language:
+        rawOutline.language ||
+        (stageInfo?.language === 'en-US'
+          ? 'en-US'
+          : stageInfo?.language === 'ru-RU'
+            ? 'ru-RU'
+            : 'zh-CN'),
+    };
 
     // ── Model resolution from request headers ──
     const { model: languageModel, modelInfo, modelString } = await resolveModelFromHeaders(req);

diff --git a/app/api/generate/scene-outlines-stream/route.ts b/app/api/generate/scene-outlines-stream/route.ts
@@ -6,9 +6,8 @@
  * so the frontend can display them incrementally.
  *
  * SSE events:
- *   { type: 'languageDirective', data: string }
  *   { type: 'outline', data: SceneOutline, index: number }
- *   { type: 'done', outlines: SceneOutline[], languageDirective: string }
+ *   { type: 'done', outlines: SceneOutline[] }
  *   { type: 'error', error: string }
  */
 
@@ -38,45 +37,33 @@ const log = createLogger('Outlines Stream');
 
 export const maxDuration = 300;
 
-/**
- * Extract the languageDirective from the streamed wrapper JSON.
- * Matches `"languageDirective":"<value>"` in partial JSON like:
- *   {"languageDirective":"用中文授课...","outlines":[...
- */
-function extractLanguageDirective(buffer: string): string | null {
-  const match = buffer.match(/"languageDirective"\s*:\s*"((?:[^"\\]|\\.)*)"/);
-  if (!match) return null;
-  try {
-    return JSON.parse(`"${match[1]}"`);
-  } catch {
-    return match[1];
+function getLocalizedEmpty(language: string, kind: 'images' | 'content' | 'research'): string {
+  if (language === 'zh-CN') {
+    return kind === 'images' ? '无可用图片' : '无';
   }
+  if (language === 'ru-RU') {
+    return kind === 'images' ? 'Нет доступных изображений' : 'Нет';
+  }
+  return kind === 'images' ? 'No images available' : 'None';
+}
+
+function resolveRequirementLanguage(language?: string): 'zh-CN' | 'en-US' | 'ru-RU' {
+  if (language === 'en-US') return 'en-US';
+  if (language === 'ru-RU') return 'ru-RU';
+  return 'zh-CN';
 }
 
 /**
  * Incremental JSON array parser.
  * Extracts complete top-level objects from a partially-streamed JSON array.
- * Supports both a flat array `[{...},{...}]` and a wrapper object
- * `{"languageDirective":"...","outlines":[{...},{...}]}`.
  * Returns newly found objects (skipping `alreadyParsed` count).
  */
 function extractNewOutlines(buffer: string, alreadyParsed: number): SceneOutline[] {
   const results: SceneOutline[] = [];
 
-  // Strip markdown fencing if present
-  const stripped = buffer.replace(/^[\s\S]*?(?=[\[{])/, '');
-
-  // Find the outlines array — either nested in {"outlines": [...]} or a flat array
-  let arrayStart = -1;
-  const outlinesKeyIdx = stripped.indexOf('"outlines"');
-  if (outlinesKeyIdx >= 0) {
-    // Wrapper format: find [ after "outlines":
-    arrayStart = stripped.indexOf('[', outlinesKeyIdx);
-  } else {
-    // Flat array fallback
-    arrayStart = stripped.indexOf('[');
-  }
-
+  // Find the start of the JSON array (skip any markdown fencing)
+  const stripped = buffer.replace(/^[\s\S]*?(?=\[)/, '');
+  const arrayStart = stripped.indexOf('[');
   if (arrayStart === -1) return results;
 
   let depth = 0;
@@ -149,17 +136,12 @@ export async function POST(req: NextRequest) {
     };
     requirementSnippet = requirements?.requirement?.substring(0, 60);
 
-    // Build user profile string for language inference context
-    const userProfileText =
-      requirements.userNickname || requirements.userBio
-        ? `## Student Profile\n\nStudent: ${requirements.userNickname || 'Unknown'}${requirements.userBio ? ` — ${requirements.userBio}` : ''}\n\nConsider this student's background when designing the course. Adapt difficulty, examples, and teaching approach accordingly.\n\n---`
-        : '';
-
     // Detect vision capability
     const hasVision = !!modelInfo?.capabilities?.vision;
+    const requirementLanguage = resolveRequirementLanguage(requirements.language);
 
     // Build prompt (same logic as generateSceneOutlinesFromRequirements)
-    let availableImagesText = 'No images available';
+    let availableImagesText = getLocalizedEmpty(requirementLanguage, 'images');
     let visionImages: Array<{ id: string; src: string }> | undefined;
 
     if (pdfImages && pdfImages.length > 0) {
@@ -170,9 +152,11 @@ export async function POST(req: NextRequest) {
         const textOnlySlice = allWithSrc.slice(MAX_VISION_IMAGES);
         const noSrcImages = pdfImages.filter((img) => !imageMapping[img.id]);
 
-        const visionDescriptions = visionSlice.map((img) => formatImagePlaceholder(img));
+        const visionDescriptions = visionSlice.map((img) =>
+          formatImagePlaceholder(img, requirementLanguage),
+        );
         const textDescriptions = [...textOnlySlice, ...noSrcImages].map((img) =>
-          formatImageDescription(img),
+          formatImageDescription(img, requirementLanguage),
         );
         availableImagesText = [...visionDescriptions, ...textDescriptions].join('\n');
 
@@ -184,7 +168,9 @@ export async function POST(req: NextRequest) {
         }));
       } else {
         // Text-only mode: full descriptions
-        availableImagesText = pdfImages.map((img) => formatImageDescription(img)).join('\n');
+        availableImagesText = pdfImages
+          .map((img) => formatImageDescription(img, requirementLanguage))
+          .join('\n');
       }
     }
 
@@ -208,12 +194,14 @@ export async function POST(req: NextRequest) {
 
     const prompts = buildPrompt(PROMPT_IDS.REQUIREMENTS_TO_OUTLINES, {
       requirement: requirements.requirement,
-      pdfContent: pdfText ? pdfText.substring(0, MAX_PDF_CONTENT_CHARS) : 'None',
+      language: requirementLanguage,
+      pdfContent: pdfText
+        ? pdfText.substring(0, MAX_PDF_CONTENT_CHARS)
+        : getLocalizedEmpty(requirementLanguage, 'content'),
       availableImages: availableImagesText,
-      researchContext: researchContext || 'None',
+      researchContext: researchContext || getLocalizedEmpty(requirementLanguage, 'research'),
       mediaGenerationPolicy,
       teacherContext,
-      userProfile: userProfileText,
     });
 
     if (!prompts) {
@@ -273,7 +261,6 @@ export async function POST(req: NextRequest) {
               };
 
           let parsedOutlines: SceneOutline[] = [];
-          let languageDirective: string | null = null;
           let lastError: string | undefined;
 
           for (let attempt = 1; attempt <= MAX_STREAM_RETRIES + 1; attempt++) {
@@ -282,23 +269,10 @@ export async function POST(req: NextRequest) {
 
               let fullText = '';
               parsedOutlines = [];
-              languageDirective = null;
 
               for await (const chunk of result.textStream) {
                 fullText += chunk;
 
-                // Try to extract language directive early
-                if (!languageDirective) {
-                  languageDirective = extractLanguageDirective(fullText);
-                  if (languageDirective) {
-                    const ldEvent = JSON.stringify({
-                      type: 'languageDirective',
-                      data: languageDirective,
-                    });
-                    controller.enqueue(encoder.encode(`data: ${ldEvent}\n\n`));
-                  }
-                }
-
                 // Try to extract new outlines from the accumulated text
                 const newOutlines = extractNewOutlines(fullText, parsedOutlines.length);
                 for (const outline of newOutlines) {
@@ -365,8 +339,6 @@ export async function POST(req: NextRequest) {
             const doneEvent = JSON.stringify({
               type: 'done',
               outlines: uniquifiedOutlines,
-              languageDirective:
-                languageDirective || 'Teach in the language that matches the user requirement.',
             });
             controller.enqueue(encoder.encode(`data: ${doneEvent}\n\n`));
           } else {

diff --git a/app/api/quiz-grade/route.ts b/app/api/quiz-grade/route.ts
@@ -47,20 +47,29 @@ export async function POST(req: NextRequest) {
     const { model: languageModel } = await resolveModelFromHeaders(req);
 
     const isZh = language === 'zh-CN';
+    const isRu = language === 'ru-RU';
 
     const systemPrompt = isZh
       ? `你是一位专业的教育评估专家。请根据题目和学生答案进行评分并给出简短评语。
 必须以如下 JSON 格式回复（不要包含其他内容）：
 {"score": <0到${points}的整数>, "comment": "<一两句评语>"}`
-      : `You are a professional educational assessor. Grade the student's answer and provide brief feedback.
+      : isRu
+        ? `Ты профессиональный эксперт по образовательной оценке. Оцени ответ студента и дай краткий комментарий.
+Ты должен ответить только в следующем JSON-формате, без любого другого текста:
+{"score": <целое число от 0 до ${points}>, "comment": "<одно-два предложения обратной связи>"}`
+        : `You are a professional educational assessor. Grade the student's answer and provide brief feedback.
 You must reply in the following JSON format only (no other content):
 {"score": <integer from 0 to ${points}>, "comment": "<one or two sentences of feedback>"}`;
 
     const userPrompt = isZh
       ? `题目：${question}
 满分：${points}分
 ${commentPrompt ? `评分要点：${commentPrompt}\n` : ''}学生答案：${userAnswer}`
-      : `Question: ${question}
+      : isRu
+        ? `Вопрос: ${question}
+Максимум: ${points} баллов
+${commentPrompt ? `Критерии оценивания: ${commentPrompt}\n` : ''}Ответ студента: ${userAnswer}`
+        : `Question: ${question}
 Full marks: ${points} points
 ${commentPrompt ? `Grading guidance: ${commentPrompt}\n` : ''}Student answer: ${userAnswer}`;
 
@@ -92,7 +101,9 @@ ${commentPrompt ? `Grading guidance: ${commentPrompt}\n` : ''}Student answer: ${
         score: Math.round(points * 0.5),
         comment: isZh
           ? '已作答，请参考标准答案。'
-          : 'Answer received. Please refer to the standard answer.',
+          : isRu
+            ? 'Ответ получен. Сверьтесь с эталонным ответом.'
+            : 'Answer received. Please refer to the standard answer.',
       };
     }
 

diff --git a/app/page.tsx b/app/page.tsx
@@ -54,17 +54,20 @@ import { useImportClassroom } from '@/lib/import/use-import-classroom';
 const log = createLogger('Home');
 
 const WEB_SEARCH_STORAGE_KEY = 'webSearchEnabled';
+const LANGUAGE_STORAGE_KEY = 'generationLanguage';
 const RECENT_OPEN_STORAGE_KEY = 'recentClassroomsOpen';
 
 interface FormState {
   pdfFile: File | null;
   requirement: string;
+  language: 'zh-CN' | 'en-US' | 'ru-RU';
   webSearch: boolean;
 }
 
 const initialFormState: FormState = {
   pdfFile: null,
   requirement: '',
+  language: 'zh-CN',
   webSearch: false,
 };
 
@@ -97,8 +100,19 @@ function HomePage() {
     }
     try {
       const savedWebSearch = localStorage.getItem(WEB_SEARCH_STORAGE_KEY);
+      const savedLanguage = localStorage.getItem(LANGUAGE_STORAGE_KEY);
       const updates: Partial<FormState> = {};
       if (savedWebSearch === 'true') updates.webSearch = true;
+      if (savedLanguage === 'zh-CN' || savedLanguage === 'en-US' || savedLanguage === 'ru-RU') {
+        updates.language = savedLanguage;
+      } else {
+        const navLang = navigator.language?.toLowerCase() || '';
+        updates.language = navLang.startsWith('zh')
+          ? 'zh-CN'
+          : navLang.startsWith('ru')
+            ? 'ru-RU'
+            : 'en-US';
+      }
       if (Object.keys(updates).length > 0) {
         setForm((prev) => ({ ...prev, ...updates }));
       }
@@ -198,6 +212,7 @@ function HomePage() {
     setForm((prev) => ({ ...prev, [field]: value }));
     try {
       if (field === 'webSearch') localStorage.setItem(WEB_SEARCH_STORAGE_KEY, String(value));
+      if (field === 'language') localStorage.setItem(LANGUAGE_STORAGE_KEY, String(value));
       if (field === 'requirement') updateRequirementCache(value as string);
     } catch {
       /* ignore */
@@ -257,6 +272,7 @@ function HomePage() {
       const userProfile = useUserProfileStore.getState();
       const requirements: UserRequirements = {
         requirement: form.requirement,
+        language: form.language,
         userNickname: userProfile.nickname || undefined,
         userBio: userProfile.bio || undefined,
         webSearch: form.webSearch || undefined,
@@ -503,6 +519,8 @@ function HomePage() {
             <div className="px-3 pb-3 flex items-end gap-2">
               <div className="flex-1 min-w-0">
                 <GenerationToolbar
+                  language={form.language}
+                  onLanguageChange={(lang) => updateForm('language', lang)}
                   webSearch={form.webSearch}
                   onWebSearchChange={(v) => updateForm('webSearch', v)}
                   onSettingsOpen={(section) => {

diff --git a/components/generation/generation-toolbar.tsx b/components/generation/generation-toolbar.tsx
@@ -1,7 +1,7 @@
 'use client';
 
 import { useState, useRef, useMemo } from 'react';
-import { Bot, Check, ChevronLeft, Paperclip, FileText, X, Globe2 } from 'lucide-react';
+import { Bot, Check, ChevronLeft, Globe, Paperclip, FileText, X, Globe2 } from 'lucide-react';
 import { Popover, PopoverContent, PopoverTrigger } from '@/components/ui/popover';
 import {
   Select,
@@ -29,6 +29,8 @@ const MAX_PDF_SIZE_BYTES = MAX_PDF_SIZE_MB * 1024 * 1024;
 
 // ─── Types ───────────────────────────────────────────────────
 export interface GenerationToolbarProps {
+  language: 'zh-CN' | 'en-US' | 'ru-RU';
+  onLanguageChange: (lang: 'zh-CN' | 'en-US' | 'ru-RU') => void;
   webSearch: boolean;
   onWebSearchChange: (v: boolean) => void;
   onSettingsOpen: (section?: SettingsSection) => void;
@@ -40,6 +42,8 @@ export interface GenerationToolbarProps {
 
 // ─── Component ───────────────────────────────────────────────
 export function GenerationToolbar({
+  language,
+  onLanguageChange,
   webSearch,
   onWebSearchChange,
   onSettingsOpen,
@@ -356,6 +360,24 @@ export function GenerationToolbar({
         </Tooltip>
       )}
 
+      {/* ── Language pill ── */}
+      <Tooltip>
+        <TooltipTrigger asChild>
+          <button
+            onClick={() =>
+              onLanguageChange(
+                language === 'zh-CN' ? 'ru-RU' : language === 'ru-RU' ? 'en-US' : 'zh-CN',
+              )
+            }
+            className={pillMuted}
+          >
+            <Globe className="size-3.5" />
+            <span>{language === 'zh-CN' ? '中文' : language === 'ru-RU' ? 'RU' : 'EN'}</span>
+          </button>
+        </TooltipTrigger>
+        <TooltipContent>Generation language</TooltipContent>
+      </Tooltip>
+
       {/* ── Separator ── */}
       <div className="w-px h-4 bg-border/60 mx-1" />
 

diff --git a/components/scene-renderers/quiz-view.tsx b/components/scene-renderers/quiz-view.tsx
@@ -129,7 +129,9 @@ async function gradeShortAnswerQuestion(
       aiComment:
         language === 'zh-CN'
           ? '评分服务暂时不可用，已给予基础分。'
-          : 'Grading service unavailable. Base score given.',
+          : language === 'ru-RU'
+            ? 'Сервис оценки временно недоступен. Начислен базовый балл.'
+            : 'Grading service unavailable. Base score given.',
     };
   }
 }