diff --git a/backend/src/main/java/com/aiteacher/concept/ConceptReportController.java b/backend/src/main/java/com/aiteacher/concept/ConceptReportController.java
index 83aa0cb..4b9599d 100644
--- a/backend/src/main/java/com/aiteacher/concept/ConceptReportController.java
+++ b/backend/src/main/java/com/aiteacher/concept/ConceptReportController.java
@@ -25,10 +25,12 @@ public class ConceptReportController {
     }
 
     @PostMapping
-    public ResponseEntity<ConceptReportResponse> generate(@PathVariable String id) {
+    public ResponseEntity<ConceptReportResponse> generate(
+            @PathVariable String id,
+            @RequestParam(defaultValue = "en") String language) {
         Topic topic = topicRepository.findById(id)
             .orElseThrow(() -> new NoSuchElementException("Topic not found."));
-        return ResponseEntity.ok(conceptReportService.generateReport(topic));
+        return ResponseEntity.ok(conceptReportService.generateReport(topic, language));
     }
 
     @GetMapping
diff --git a/backend/src/main/java/com/aiteacher/concept/ConceptReportService.java b/backend/src/main/java/com/aiteacher/concept/ConceptReportService.java
index 16ba3f6..c0b3a24 100644
--- a/backend/src/main/java/com/aiteacher/concept/ConceptReportService.java
+++ b/backend/src/main/java/com/aiteacher/concept/ConceptReportService.java
@@ -60,7 +60,7 @@ public class ConceptReportService {
         this.objectMapper = objectMapper;
     }
 
-    public ConceptReportResponse generateReport(Topic topic) {
+    public ConceptReportResponse generateReport(Topic topic, String language) {
         List<Book> readyBooks = bookRepository.findAll().stream()
             .filter(b -> b.getStatus() == BookStatus.READY)
             .toList();
@@ -106,7 +106,7 @@ public class ConceptReportService {
             if (mf == null || mf.isEmpty()) continue;
             if (facet == ConceptFacet.OTHER) continue; // skip OTHER bucket in the rendered report
 
-            String prompt = buildFacetPrompt(topic, facet, mf, sectionLabel, figureLabel);
+            String prompt = buildFacetPrompt(topic, facet, mf, sectionLabel, figureLabel, language);
             String markdown = chatClient.prompt()
                 .system(SYSTEM_PROMPT)
                 .user(prompt)
@@ -151,7 +151,8 @@ public class ConceptReportService {
 
     private String buildFacetPrompt(Topic topic, ConceptFacet facet, MergedFacet mf,
                                      Map<String, String> sectionLabel,
-                                     Map<String, String> figureLabel) {
+                                     Map<String, String> figureLabel,
+                                     String language) {
         StringBuilder sb = new StringBuilder();
         sb.append("CONCEPT: ").append(topic.getName()).append("\n");
         sb.append("FACET: ").append(facet.displayTitle()).append("\n\n");
@@ -181,6 +182,17 @@ public class ConceptReportService {
         sb.append("Write the ").append(facet.displayTitle()).append(" section of a concept report on \"")
           .append(topic.getName())
           .append("\". Stay strictly within this facet. Use the [S#]/[F#] labels above for citations.");
+
+        if ("th".equalsIgnoreCase(language)) {
+            sb.append("\n\nIMPORTANT: Write the narrative in Thai. ")
+              .append("Keep all medical, anatomical, surgical, pharmacological, and clinical ")
+              .append("terminology in English (e.g., cerebellopontine angle, glioblastoma, craniotomy, ")
+              .append("dexamethasone). Do NOT translate disease names, anatomical structures, drug names, ")
+              .append("procedures, eponyms, or imaging modalities. Translate only connective prose, ")
+              .append("explanations, and general descriptions. Citation labels [S#]/[F#] stay unchanged. ")
+              .append("The sentinel string for insufficient context must remain exactly: ")
+              .append("\"The uploaded books do not contain sufficient information on this aspect.\"");
+        }
         return sb.toString();
     }
 
diff --git a/backend/src/main/java/com/aiteacher/topic/TopicController.java b/backend/src/main/java/com/aiteacher/topic/TopicController.java
index 7d93672..10ddc14 100644
--- a/backend/src/main/java/com/aiteacher/topic/TopicController.java
+++ b/backend/src/main/java/com/aiteacher/topic/TopicController.java
@@ -26,11 +26,13 @@ public class TopicController {
     }
 
     @PostMapping("/{id}/summary")
-    public ResponseEntity<TopicSummaryResponse> generateSummary(@PathVariable String id) {
+    public ResponseEntity<TopicSummaryResponse> generateSummary(
+            @PathVariable String id,
+            @RequestParam(defaultValue = "en") String language) {
         Topic topic = topicRepository.findById(id)
             .orElseThrow(() -> new NoSuchElementException("Topic not found."));
 
-        TopicSummaryResponse response = topicSummaryService.generateSummary(topic);
+        TopicSummaryResponse response = topicSummaryService.generateSummary(topic, language);
         return ResponseEntity.ok(response);
     }
 
diff --git a/backend/src/main/java/com/aiteacher/topic/TopicSummaryService.java b/backend/src/main/java/com/aiteacher/topic/TopicSummaryService.java
index 3b3ca37..37a0fee 100644
--- a/backend/src/main/java/com/aiteacher/topic/TopicSummaryService.java
+++ b/backend/src/main/java/com/aiteacher/topic/TopicSummaryService.java
@@ -59,7 +59,7 @@ public class TopicSummaryService {
         this.objectMapper = objectMapper;
     }
 
-    public TopicSummaryResponse generateSummary(Topic topic) {
+    public TopicSummaryResponse generateSummary(Topic topic, String language) {
         List<Book> readyBooks = bookRepository.findAll().stream()
             .filter(b -> b.getStatus() == BookStatus.READY)
             .toList();
@@ -82,7 +82,7 @@ public class TopicSummaryService {
         log.debug("Topic reports for '{}': {} sections, {} figures retrieved",
             topic.getName(), allSections.size(), allFigures.size());
 
-        String contextPrompt = buildContextPrompt(question, allSections, allFigures);
+        String contextPrompt = buildContextPrompt(question, allSections, allFigures, language);
         String summary = chatClient.prompt()
             .system(SYSTEM_PROMPT)
             .user(contextPrompt)
@@ -142,7 +142,8 @@ public class TopicSummaryService {
 
     private String buildContextPrompt(String question,
                                       List<SectionEntity> sections,
-                                      List<FigureEntity> figures) {
+                                      List<FigureEntity> figures,
+                                      String language) {
         StringBuilder sb = new StringBuilder();
 
         if (!sections.isEmpty()) {
@@ -169,6 +170,17 @@ public class TopicSummaryService {
         }
 
         sb.append("QUESTION:\n").append(question);
+
+        if ("th".equalsIgnoreCase(language)) {
+            sb.append("\n\nIMPORTANT: Write the narrative in Thai. ")
+              .append("Keep all medical, anatomical, surgical, pharmacological, and clinical ")
+              .append("terminology in English (e.g., cerebellopontine angle, glioblastoma, craniotomy, ")
+              .append("dexamethasone). Do NOT translate disease names, anatomical structures, drug names, ")
+              .append("procedures, eponyms, or imaging modalities. Translate only connective prose, ")
+              .append("explanations, and general descriptions. Citation labels [S#]/[F#] stay unchanged. ")
+              .append("The sentinel string for insufficient context must remain exactly: ")
+              .append("\"The uploaded books do not contain sufficient information on this topic.\"");
+        }
         return sb.toString();
     }
 
diff --git a/frontend/src/components/BookCard.vue b/frontend/src/components/BookCard.vue
index 879aefa..3586105 100644
--- a/frontend/src/components/BookCard.vue
+++ b/frontend/src/components/BookCard.vue
@@ -48,7 +48,7 @@
         Read
       </router-link>
       <button
-        v-if="book.status === 'READY'"
+        v-if="book.status === 'READY' && uploadEnabled"
         class="btn btn-secondary"
         :disabled="enrichRunning"
         @click="handleEnrich"
@@ -73,6 +73,7 @@
 import { computed, onUnmounted, ref } from 'vue'
 import type { Book, EnrichmentProgress } from '@/stores/bookStore'
 import { useBookStore } from '@/stores/bookStore'
+import { env } from '@/env';
 
 const props = defineProps<{
   book: Book
@@ -90,6 +91,7 @@ const enrichFeedback = ref<string | null>(null)
 let pollTimer: ReturnType<typeof setInterval> | null = null
 
 const enrichRunning = computed(() => enrichProgress.value?.status === 'RUNNING')
+const uploadEnabled = env('VITE_UPLOAD_ENABLED') !== 'false'
 
 async function handleEnrich() {
   enrichFeedback.value = null
diff --git a/frontend/src/stores/topicStore.ts b/frontend/src/stores/topicStore.ts
index 961a0e4..7499d4b 100644
--- a/frontend/src/stores/topicStore.ts
+++ b/frontend/src/stores/topicStore.ts
@@ -120,13 +120,17 @@ export const useTopicStore = defineStore('topics', () => {
     }
   }
 
-  async function generateSummary(topicId: string): Promise<TopicSummary | null> {
+  async function generateSummary(topicId: string, language: 'en' | 'th' = 'en'): Promise<TopicSummary | null> {
     summaryLoading.value = true
     activeSummaryTopicId.value = topicId
     activeSummary.value = null
     error.value = null
     try {
-      const response = await api.post<TopicSummary>(`/topics/${topicId}/summary`)
+      const response = await api.post<TopicSummary>(
+        `/topics/${topicId}/summary`,
+        null,
+        { params: { language } }
+      )
       activeSummary.value = response.data
       return response.data
     } catch (err: any) {
@@ -168,12 +172,16 @@ export const useTopicStore = defineStore('topics', () => {
     }
   }
 
-  async function generateConceptReport(topicId: string): Promise<ConceptReport | null> {
+  async function generateConceptReport(topicId: string, language: 'en' | 'th' = 'en'): Promise<ConceptReport | null> {
     conceptReportLoading.value = true
     activeConceptReport.value = null
     error.value = null
     try {
-      const response = await api.post<ConceptReport>(`/topics/${topicId}/concept-reports`)
+      const response = await api.post<ConceptReport>(
+        `/topics/${topicId}/concept-reports`,
+        null,
+        { params: { language } }
+      )
       activeConceptReport.value = response.data
       return response.data
     } catch (err: any) {
diff --git a/frontend/src/views/TopicsView.vue b/frontend/src/views/TopicsView.vue
index 683cdf1..8a09e9d 100644
--- a/frontend/src/views/TopicsView.vue
+++ b/frontend/src/views/TopicsView.vue
@@ -38,10 +38,28 @@
         <div v-if="selectedTopicId && mode === 'summary'" class="history-panel card">
           <div class="history-header">
             <span class="history-title">Saved summaries</span>
-            <button class="btn btn-primary btn-sm" :disabled="topicStore.summaryLoading" @click="handleGenerate(selectedTopicId!)">
-              <span v-if="topicStore.summaryLoading" class="spinner" style="width:14px;height:14px;display:inline-block;vertical-align:middle;margin-right:4px;"></span>
-              Generate New
-            </button>
+            <div class="history-actions">
+              <div class="lang-toggle" role="group" aria-label="Summary language">
+                <button
+                  type="button"
+                  class="lang-toggle-btn"
+                  :class="{ 'lang-toggle-btn--active': summaryLanguage === 'en' }"
+                  :disabled="topicStore.summaryLoading"
+                  @click="summaryLanguage = 'en'"
+                >EN</button>
+                <button
+                  type="button"
+                  class="lang-toggle-btn"
+                  :class="{ 'lang-toggle-btn--active': summaryLanguage === 'th' }"
+                  :disabled="topicStore.summaryLoading"
+                  @click="summaryLanguage = 'th'"
+                >TH</button>
+              </div>
+              <button class="btn btn-primary btn-sm" :disabled="topicStore.summaryLoading" @click="handleGenerate(selectedTopicId!)">
+                <span v-if="topicStore.summaryLoading" class="spinner" style="width:14px;height:14px;display:inline-block;vertical-align:middle;margin-right:4px;"></span>
+                Generate New
+              </button>
+            </div>
           </div>
 
           <div v-if="topicStore.summaryListLoading" class="history-loading">
@@ -71,10 +89,28 @@
         <div v-if="selectedTopicId && mode === 'concept'" class="history-panel card">
           <div class="history-header">
             <span class="history-title">Saved concept reports</span>
-            <button class="btn btn-primary btn-sm" :disabled="topicStore.conceptReportLoading" @click="handleGenerateConcept(selectedTopicId!)">
-              <span v-if="topicStore.conceptReportLoading" class="spinner" style="width:14px;height:14px;display:inline-block;vertical-align:middle;margin-right:4px;"></span>
-              Generate New
-            </button>
+            <div class="history-actions">
+              <div class="lang-toggle" role="group" aria-label="Report language">
+                <button
+                  type="button"
+                  class="lang-toggle-btn"
+                  :class="{ 'lang-toggle-btn--active': conceptLanguage === 'en' }"
+                  :disabled="topicStore.conceptReportLoading"
+                  @click="conceptLanguage = 'en'"
+                >EN</button>
+                <button
+                  type="button"
+                  class="lang-toggle-btn"
+                  :class="{ 'lang-toggle-btn--active': conceptLanguage === 'th' }"
+                  :disabled="topicStore.conceptReportLoading"
+                  @click="conceptLanguage = 'th'"
+                >TH</button>
+              </div>
+              <button class="btn btn-primary btn-sm" :disabled="topicStore.conceptReportLoading" @click="handleGenerateConcept(selectedTopicId!)">
+                <span v-if="topicStore.conceptReportLoading" class="spinner" style="width:14px;height:14px;display:inline-block;vertical-align:middle;margin-right:4px;"></span>
+                Generate New
+              </button>
+            </div>
           </div>
 
           <div v-if="topicStore.conceptReportListLoading" class="history-loading">
@@ -269,6 +305,8 @@ const showSources = ref(true)
 const summaryError = ref<string | null>(null)
 const conceptError = ref<string | null>(null)
 const isNoBooks = ref(false)
+const conceptLanguage = ref<'en' | 'th'>('en')
+const summaryLanguage = ref<'en' | 'th'>('en')
 const sourcesSection = ref<HTMLElement | null>(null)
 const selectedTopicId = ref<string | null>(null)
 const mode = ref<'summary' | 'concept'>('summary')
@@ -401,7 +439,7 @@ async function handleGenerateConcept(topicId: string) {
   conceptError.value = null
   isNoBooks.value = false
   showSources.value = true
-  const result = await topicStore.generateConceptReport(topicId)
+  const result = await topicStore.generateConceptReport(topicId, conceptLanguage.value)
   if (!result) {
     conceptError.value = topicStore.error ?? 'Failed to generate concept report.'
     isNoBooks.value =
@@ -425,7 +463,7 @@ async function handleGenerate(topicId: string) {
   isNoBooks.value = false
   showSources.value = true
 
-  const result = await topicStore.generateSummary(topicId)
+  const result = await topicStore.generateSummary(topicId, summaryLanguage.value)
   if (!result) {
     summaryError.value = topicStore.error ?? 'Failed to generate summary.'
     isNoBooks.value =
@@ -528,6 +566,52 @@ function formatDateShort(iso: string): string {
   margin-bottom: 0.75rem;
 }
 
+.history-actions {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+}
+
+.lang-toggle {
+  display: inline-flex;
+  border: 1px solid var(--border-color, #d0d7de);
+  border-radius: 6px;
+  overflow: hidden;
+}
+
+.lang-toggle-btn {
+  padding: 0.25rem 0.55rem;
+  font-size: 0.75rem;
+  font-weight: 600;
+  background: transparent;
+  color: var(--text-secondary, #57606a);
+  border: none;
+  cursor: pointer;
+  line-height: 1;
+}
+
+.lang-toggle-btn:not(:last-child) {
+  border-right: 1px solid var(--border-color, #d0d7de);
+}
+
+.lang-toggle-btn:hover:not(:disabled) {
+  background: var(--hover-bg, #f3f4f6);
+}
+
+.lang-toggle-btn--active {
+  background: var(--primary-color, #0969da);
+  color: #fff;
+}
+
+.lang-toggle-btn--active:hover:not(:disabled) {
+  background: var(--primary-color, #0969da);
+}
+
+.lang-toggle-btn:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+}
+
 .history-title {
   font-size: 0.875rem;
   font-weight: 600;