feat: localize interview questions (ko/en), send X-Lang header

internal/httpapi/diagnostic.go

@@ -13,6 +13,7 @@ type createDiagnosticSessionRequest struct {
 	TargetRole        string   `json:"target_role"`
 	Stack             []string `json:"stack"`
 	InterviewTimeline string   `json:"interview_timeline"`
+	Lang              string   `json:"lang"`
 }
 
 type submitDiagnosticAnswerRequest struct {
@@ -27,11 +28,19 @@ func (h Handler) createDiagnosticSession(w http.ResponseWriter, r *http.Request)
 		return
 	}
 
+	lang := req.Lang
+	if lang == "" {
+		lang = r.Header.Get("X-Lang")
+	}
+	if lang == "" {
+		lang = "en"
+	}
 	session, err := h.diagnostic.CreateSession(r.Context(), interview.CreateSessionInput{
 		UserID:            req.UserID,
 		TargetRole:        req.TargetRole,
 		Stack:             req.Stack,
 		InterviewTimeline: req.InterviewTimeline,
+		Lang:              lang,
 	})
 	if err != nil {
 		writeError(w, http.StatusBadRequest, err.Error())

internal/interview/catalog.go

@@ -2,28 +2,49 @@ package interview
 
 import "tutor/internal/workflows"
 
-func BackendDeveloperQuestions() []Question {
+var questionPrompts = map[string]map[string]string{
-	return []Question{
+	"ko": {
+		"backend-http-idempotency": "HTTP 메서드가 멱등성을 가지려면 어떤 조건이 필요하며, 재시도 시 왜 중요한가요?",
+		"backend-db-index-tradeoff": "데이터베이스 인덱스를 추가하면 API가 어떻게 개선되며, 어떤 트레이드오프가 발생할 수 있나요?",
+		"backend-cache-invalidation": "API 응답을 캐싱할지 어떻게 결정하며, 오래된 데이터는 어떻게 처리하나요?",
+	},
+	"en": {
+		"backend-http-idempotency": "What makes an HTTP method idempotent, and why does that matter for retries?",
+		"backend-db-index-tradeoff": "When would adding a database index improve an API, and what tradeoffs can it introduce?",
+		"backend-cache-invalidation": "How would you decide whether to cache an API response, and how would you handle stale data?",
+	},
+}
+
+func BackendDeveloperQuestions(lang string) []Question {
+	if lang == "" {
+		lang = "en"
+	}
+	base := []Question{
 		{
-			ID:     "backend-http-idempotency",
+			ID: "backend-http-idempotency",
-			Prompt: "What makes an HTTP method idempotent, and why does that matter for retries?",
 			Concepts: []workflows.ConceptRef{
 				{ID: "http-idempotency", Label: "HTTP idempotency", Track: BackendDeveloperTrack},
 			},
 		},
 		{
-			ID:     "backend-db-index-tradeoff",
+			ID: "backend-db-index-tradeoff",
-			Prompt: "When would adding a database index improve an API, and what tradeoffs can it introduce?",
 			Concepts: []workflows.ConceptRef{
 				{ID: "database-indexes", Label: "Database indexes", Track: BackendDeveloperTrack},
 			},
 		},
 		{
-			ID:     "backend-cache-invalidation",
+			ID: "backend-cache-invalidation",
-			Prompt: "How would you decide whether to cache an API response, and how would you handle stale data?",
 			Concepts: []workflows.ConceptRef{
 				{ID: "cache-invalidation", Label: "Cache invalidation", Track: BackendDeveloperTrack},
 			},
 		},
 	}
+	for i := range base {
+		if p, ok := questionPrompts[lang][base[i].ID]; ok {
+			base[i].Prompt = p
+		} else if p, ok := questionPrompts["en"][base[i].ID]; ok {
+			base[i].Prompt = p
+		}
+	}
+	return base
 }

internal/interview/service.go

@@ -44,7 +44,7 @@ func (s *Service) CreateSession(_ context.Context, input CreateSessionInput) (Se
 		TargetRole:        input.TargetRole,
 		Stack:             append([]string(nil), input.Stack...),
 		InterviewTimeline: input.InterviewTimeline,
-		Questions:         BackendDeveloperQuestions(),
+		Questions:         BackendDeveloperQuestions(input.Lang),
 		CreatedAt:         time.Now().UTC(),
 	}
 	if s.memory != nil {

internal/interview/types.go

@@ -47,6 +47,7 @@ type CreateSessionInput struct {
 	TargetRole        string
 	Stack             []string
 	InterviewTimeline string
+	Lang              string
 }
 
 type SubmitAnswerInput struct {

internal/webapp/static/app.js

@@ -89,6 +89,7 @@ els.sessionForm.addEventListener("submit", async (event) => {
       .map((item) => item.trim())
       .filter(Boolean),
     interview_timeline: value("#timeline"),
+    lang: localStorage.getItem("tutor_lang") || document.documentElement.lang || "ko",
   };
 
   try {
@@ -216,7 +217,7 @@ function renderSession() {
       "aria-pressed",
       String(state.selectedQuestion?.id === question.id)
     );
-    button.innerHTML = `<span class="question-id">${escapeHTML(question.id)}</span>${escapeHTML(question.prompt)}`;
+    button.innerHTML = `<span class="question-id">${escapeHTML(question.id)}</span>${escapeHTML(tq(question.id) || question.prompt)}`;
     button.addEventListener("click", () => {
       state.selectedQuestion = question;
       els.answerText.value = "";
@@ -465,7 +466,8 @@ els.logoutButton.addEventListener("click", () => {
 
 async function request(url, options = {}) {
   const token = localStorage.getItem("tutor_token");
-  const headers = { "Content-Type": "application/json" };
+  const lang = localStorage.getItem("tutor_lang") || document.documentElement.lang || "ko";
+  const headers = { "Content-Type": "application/json", "X-Lang": lang };
   if (token) headers["Authorization"] = `Bearer ${token}`;
   const response = await fetch(url, { headers, ...options });
   const body = await response.json();

internal/webapp/static/i18n.js

@@ -181,6 +181,33 @@ window.t = function (key, ...args) {
   return typeof text === "function" ? text(...args) : text;
 }
 
+var questionTexts = {
+  ko: {
+    "backend-http-idempotency":
+      "HTTP 메서드가 멱등성을 가지려면 어떤 조건이 필요하며, 재시도 시 왜 중요한가요?",
+    "backend-db-index-tradeoff":
+      "데이터베이스 인덱스를 추가하면 API가 어떻게 개선되며, 어떤 트레이드오프가 발생할 수 있나요?",
+    "backend-cache-invalidation":
+      "API 응답을 캐싱할지 어떻게 결정하며, 오래된 데이터는 어떻게 처리하나요?",
+  },
+  en: {
+    "backend-http-idempotency":
+      "What makes an HTTP method idempotent, and why does that matter for retries?",
+    "backend-db-index-tradeoff":
+      "When would adding a database index improve an API, and what tradeoffs can it introduce?",
+    "backend-cache-invalidation":
+      "How would you decide whether to cache an API response, and how would you handle stale data?",
+  },
+};
+
+window.tq = function (id) {
+  const lang =
+    localStorage.getItem("tutor_lang") ||
+    document.documentElement.lang ||
+    "ko";
+  return questionTexts[lang]?.[id] ?? questionTexts["en"]?.[id] ?? "";
+};
+
 window.updateStaticText = function () {
   const lang =
     localStorage.getItem("tutor_lang") ||