diff --git a/CHANGELOG.md b/CHANGELOG.md
index 86533e1da..964512cbc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Localized quest text (phase B of [#188](https://github.com/Mezeporta/Erupe/issues/188)): quest JSON `title`, `description`, `text_main`, `text_sub_a`, `text_sub_b`, `success_cond`, `fail_cond`, and `contractor` now accept either a plain string (existing behaviour, single-language) or a language-keyed object like `{"jp": "...", "en": "...", "fr": "..."}`. `CompileQuestJSON` takes the requesting session's language and resolves each field with a fallback chain (requested → plain → jp → en → any non-empty). The quest cache is now keyed by `(questID, language)` so compiled binaries for different languages never leak between sessions. `ParseQuestBinary` emits plain strings unchanged, so round-tripping existing `.bin` files through the JSON path produces byte-identical output. New `LocalizedString` type is reusable for phase C (scenarios, mail, shop). Shift-JIS encoding limits still apply — localized strings must use characters representable in Shift-JIS (ASCII, kana, CJK).
 - Per-session language preference (phase A of [#188](https://github.com/Mezeporta/Erupe/issues/188)): new `users.language` column (migration `0022_user_language`), `UserRepo.GetLanguage`/`SetLanguage`, `Session.Lang()`/`SetLang()` accessors, and a `!lang <en|jp|fr|es>` command to show or change the session's language live. The preference is loaded on login and persisted across sessions; an empty value falls back to `config.Language`. The `getLangStringsFor(code)` primitive is the new way to resolve an i18n table from a concrete code — existing callers keep working via the unchanged `getLangStrings(server)` wrapper. This is plumbing only: localized quest/scenario content comes in phase B.
 
 ### Changed
diff --git a/server/channelserver/handlers_quest.go b/server/channelserver/handlers_quest.go
index 6a6428ecc..2ac1bd90a 100644
--- a/server/channelserver/handlers_quest.go
+++ b/server/channelserver/handlers_quest.go
@@ -161,7 +161,7 @@ func loadQuestBinary(s *Session, filename string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	compiled, err := CompileQuestJSON(jsonData)
+	compiled, err := CompileQuestJSON(jsonData, s.Lang())
 	if err != nil {
 		return nil, fmt.Errorf("compile quest JSON %s: %w", filename, err)
 	}
@@ -248,7 +248,8 @@ func handleMsgMhfSaveFavoriteQuest(s *Session, p mhfpacket.MHFPacket) {
 }
 
 func loadQuestFile(s *Session, questId int) []byte {
-	if cached, ok := s.server.questCache.Get(questId); ok {
+	lang := s.Lang()
+	if cached, ok := s.server.questCache.Get(questId, lang); ok {
 		return cached
 	}
 
@@ -257,7 +258,7 @@ func loadQuestFile(s *Session, questId int) []byte {
 	if data, err := os.ReadFile(base + ".bin"); err == nil {
 		decrypted = decryption.UnpackSimple(data)
 	} else if jsonData, err := os.ReadFile(base + ".json"); err == nil {
-		compiled, err := CompileQuestJSON(jsonData)
+		compiled, err := CompileQuestJSON(jsonData, lang)
 		if err != nil {
 			s.logger.Error("loadQuestFile: failed to compile quest JSON",
 				zap.Int("questId", questId), zap.Error(err))
@@ -313,7 +314,7 @@ func loadQuestFile(s *Session, questId int) []byte {
 	questBody.WriteBytes(newStrings.Data())
 
 	result := questBody.Data()
-	s.server.questCache.Put(questId, result)
+	s.server.questCache.Put(questId, lang, result)
 	return result
 }
 
diff --git a/server/channelserver/localized_string.go b/server/channelserver/localized_string.go
new file mode 100644
index 000000000..8979fe74c
--- /dev/null
+++ b/server/channelserver/localized_string.go
@@ -0,0 +1,103 @@
+package channelserver
+
+import (
+	"bytes"
+	"encoding/json"
+)
+
+// LocalizedString is a JSON field that unmarshals from either a plain string
+// (backwards-compatible single-language behaviour — the value is returned for
+// every language) or a map keyed by language code, e.g.
+//
+//	"title": "リオレウス"
+//	"title": { "jp": "リオレウス", "en": "Rathalos", "fr": "Rathalos" }
+//
+// It is the core primitive used by phase B of #188 to localize server-sent
+// content (quest text, scenario strings, mail templates, ...) per session
+// without breaking any existing single-language JSON file.
+//
+// Encoding note: strings that end up on the wire as Shift-JIS (quest text,
+// scenario strings) must only use characters representable in Shift-JIS —
+// ASCII, kana, and CJK. Latin-extended characters commonly used in European
+// languages (ê, ñ, ß, ...) will be rejected by the encoder at compile time.
+// For those languages prefer ASCII-only romanizations ("Quete de test",
+// "Espana") until the Frontier binary protocol is extended to a wider
+// encoding.
+type LocalizedString struct {
+	// plain is set when the source was a bare JSON string. Treated as the
+	// fallback for every language so legacy single-language files keep
+	// working with no schema change.
+	plain string
+	// values is set when the source was a JSON object. Keys are language
+	// codes (lowercase, e.g. "jp", "en", "fr", "es").
+	values map[string]string
+}
+
+// NewLocalizedPlain wraps a single-language string — used internally by the
+// binary-to-JSON reverse path (ParseQuestBinary etc.) where only one language
+// is available from the source file.
+func NewLocalizedPlain(s string) LocalizedString {
+	return LocalizedString{plain: s}
+}
+
+// UnmarshalJSON accepts either a JSON string or a JSON object.
+func (l *LocalizedString) UnmarshalJSON(data []byte) error {
+	trimmed := bytes.TrimSpace(data)
+	if len(trimmed) == 0 || bytes.Equal(trimmed, []byte("null")) {
+		return nil
+	}
+	if trimmed[0] == '"' {
+		return json.Unmarshal(trimmed, &l.plain)
+	}
+	return json.Unmarshal(trimmed, &l.values)
+}
+
+// MarshalJSON round-trips: plain strings stay plain; maps stay maps. This
+// matters for the reverse ParseQuestBinary → JSON path, which should produce
+// a plain string (backwards compatible), and for hypothetical editor tooling
+// that reads a localized JSON, mutates it, and writes it back unchanged.
+func (l LocalizedString) MarshalJSON() ([]byte, error) {
+	if l.values != nil {
+		return json.Marshal(l.values)
+	}
+	return json.Marshal(l.plain)
+}
+
+// Resolve returns the best available string for the requested language code.
+// Fallback order when the requested language is missing:
+//  1. The plain-string form (single-language source)
+//  2. jp (the canonical source language for MH Frontier)
+//  3. en (the common secondary)
+//  4. Any non-empty value in the map
+//
+// Returns "" only when nothing is set — callers that need a non-empty value
+// for binary serialization should treat that as an empty quest string, which
+// the existing toShiftJIS encoder already accepts.
+func (l LocalizedString) Resolve(lang string) string {
+	if l.values == nil {
+		return l.plain
+	}
+	if v, ok := l.values[lang]; ok && v != "" {
+		return v
+	}
+	if l.plain != "" {
+		return l.plain
+	}
+	for _, fb := range []string{"jp", "en"} {
+		if v, ok := l.values[fb]; ok && v != "" {
+			return v
+		}
+	}
+	for _, v := range l.values {
+		if v != "" {
+			return v
+		}
+	}
+	return ""
+}
+
+// IsLocalized reports whether the value was written as a language map (rather
+// than a plain string). Mostly useful for tests and tooling.
+func (l LocalizedString) IsLocalized() bool {
+	return l.values != nil
+}
diff --git a/server/channelserver/localized_string_test.go b/server/channelserver/localized_string_test.go
new file mode 100644
index 000000000..ed92b9ac8
--- /dev/null
+++ b/server/channelserver/localized_string_test.go
@@ -0,0 +1,149 @@
+package channelserver
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestLocalizedString_UnmarshalPlainString(t *testing.T) {
+	var l LocalizedString
+	if err := json.Unmarshal([]byte(`"Rathalos"`), &l); err != nil {
+		t.Fatalf("unmarshal plain: %v", err)
+	}
+	if l.IsLocalized() {
+		t.Error("plain string should not be IsLocalized")
+	}
+	// Plain strings resolve to the same value regardless of language — this
+	// is the backwards-compatibility contract that keeps existing single-
+	// language quest JSONs working without a schema migration.
+	for _, lang := range []string{"", "jp", "en", "fr", "es", "klingon"} {
+		if got := l.Resolve(lang); got != "Rathalos" {
+			t.Errorf("Resolve(%q) = %q, want %q", lang, got, "Rathalos")
+		}
+	}
+}
+
+func TestLocalizedString_UnmarshalMap(t *testing.T) {
+	var l LocalizedString
+	src := `{"jp": "リオレウス", "en": "Rathalos", "fr": "Rathalos"}`
+	if err := json.Unmarshal([]byte(src), &l); err != nil {
+		t.Fatalf("unmarshal map: %v", err)
+	}
+	if !l.IsLocalized() {
+		t.Error("map form should be IsLocalized")
+	}
+	cases := map[string]string{
+		"jp": "リオレウス",
+		"en": "Rathalos",
+		"fr": "Rathalos",
+	}
+	for lang, want := range cases {
+		if got := l.Resolve(lang); got != want {
+			t.Errorf("Resolve(%q) = %q, want %q", lang, got, want)
+		}
+	}
+}
+
+func TestLocalizedString_ResolveFallbackChain(t *testing.T) {
+	// Spanish not provided — should fall back to jp first (canonical source
+	// language for MHF), then en, then any non-empty.
+	var l LocalizedString
+	if err := json.Unmarshal([]byte(`{"jp": "リオレウス", "en": "Rathalos"}`), &l); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if got := l.Resolve("es"); got != "リオレウス" {
+		t.Errorf("missing-lang fallback = %q, want jp value %q", got, "リオレウス")
+	}
+
+	// Only en provided → en must win even when jp is requested.
+	var l2 LocalizedString
+	if err := json.Unmarshal([]byte(`{"en": "Rathalos"}`), &l2); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if got := l2.Resolve("jp"); got != "Rathalos" {
+		t.Errorf("jp-missing fallback = %q, want %q", got, "Rathalos")
+	}
+
+	// Neither jp nor en → any non-empty value.
+	var l3 LocalizedString
+	if err := json.Unmarshal([]byte(`{"fr": "Rathalos FR"}`), &l3); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if got := l3.Resolve("jp"); got != "Rathalos FR" {
+		t.Errorf("last-resort fallback = %q, want %q", got, "Rathalos FR")
+	}
+
+	// Empty string entries are skipped by the fallback chain.
+	var l4 LocalizedString
+	if err := json.Unmarshal([]byte(`{"jp": "", "en": "Rathalos"}`), &l4); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if got := l4.Resolve("fr"); got != "Rathalos" {
+		t.Errorf("empty-jp fallback = %q, want %q (should skip empty jp)", got, "Rathalos")
+	}
+}
+
+func TestLocalizedString_EmptyResolvesEmpty(t *testing.T) {
+	var l LocalizedString
+	if got := l.Resolve("jp"); got != "" {
+		t.Errorf("zero value Resolve = %q, want empty", got)
+	}
+}
+
+func TestLocalizedString_MarshalRoundTrip(t *testing.T) {
+	// Plain string round-trip.
+	var plain LocalizedString
+	if err := json.Unmarshal([]byte(`"Rathalos"`), &plain); err != nil {
+		t.Fatal(err)
+	}
+	out, err := json.Marshal(plain)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(out) != `"Rathalos"` {
+		t.Errorf("plain round-trip = %s, want %q", out, "Rathalos")
+	}
+
+	// Map round-trip.
+	var m LocalizedString
+	if err := json.Unmarshal([]byte(`{"en":"Rathalos","jp":"リオレウス"}`), &m); err != nil {
+		t.Fatal(err)
+	}
+	out, err = json.Marshal(m)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Unmarshal again and compare — map key order is unstable so we don't
+	// string-compare the marshaled form directly.
+	var back LocalizedString
+	if err := json.Unmarshal(out, &back); err != nil {
+		t.Fatal(err)
+	}
+	if got := back.Resolve("jp"); got != "リオレウス" {
+		t.Errorf("round-trip jp = %q", got)
+	}
+	if got := back.Resolve("en"); got != "Rathalos" {
+		t.Errorf("round-trip en = %q", got)
+	}
+}
+
+func TestLocalizedString_NullUnmarshal(t *testing.T) {
+	// JSON null → zero value, no error.
+	var l LocalizedString
+	if err := json.Unmarshal([]byte(`null`), &l); err != nil {
+		t.Fatalf("unmarshal null: %v", err)
+	}
+	if l.IsLocalized() || l.Resolve("") != "" {
+		t.Error("null should produce zero LocalizedString")
+	}
+}
+
+func TestNewLocalizedPlain(t *testing.T) {
+	l := NewLocalizedPlain("hello")
+	if l.IsLocalized() {
+		t.Error("NewLocalizedPlain should not be IsLocalized")
+	}
+	if got := l.Resolve("jp"); got != "hello" {
+		t.Errorf("Resolve = %q, want %q", got, "hello")
+	}
+}
diff --git a/server/channelserver/quest_cache.go b/server/channelserver/quest_cache.go
index c36e781be..248437bd2 100644
--- a/server/channelserver/quest_cache.go
+++ b/server/channelserver/quest_cache.go
@@ -5,11 +5,22 @@ import (
 	"time"
 )
 
-// QuestCache is a thread-safe, expiring cache for parsed quest file data.
+// questCacheKey identifies a cached quest variant. Phase B of #188 added the
+// language dimension so localized quest text compiled for one session does
+// not leak into another session's response.
+type questCacheKey struct {
+	questID int
+	lang    string
+}
+
+// QuestCache is a thread-safe, expiring cache for parsed quest file data,
+// keyed by (questID, language). Entries for different languages are stored
+// independently so a Japanese client and a French client on the same server
+// never share compiled binaries.
 type QuestCache struct {
 	mu     sync.RWMutex
-	data   map[int][]byte
-	expiry map[int]time.Time
+	data   map[questCacheKey][]byte
+	expiry map[questCacheKey]time.Time
 	ttl    time.Duration
 }
 
@@ -17,33 +28,36 @@ type QuestCache struct {
 // A TTL of 0 disables caching (Get always misses).
 func NewQuestCache(ttlSeconds int) *QuestCache {
 	return &QuestCache{
-		data:   make(map[int][]byte),
-		expiry: make(map[int]time.Time),
+		data:   make(map[questCacheKey][]byte),
+		expiry: make(map[questCacheKey]time.Time),
 		ttl:    time.Duration(ttlSeconds) * time.Second,
 	}
 }
 
-// Get returns cached quest data if it exists and has not expired.
-func (c *QuestCache) Get(questID int) ([]byte, bool) {
+// Get returns cached quest data for the (questID, lang) variant if it exists
+// and has not expired.
+func (c *QuestCache) Get(questID int, lang string) ([]byte, bool) {
 	if c.ttl <= 0 {
 		return nil, false
 	}
+	k := questCacheKey{questID: questID, lang: lang}
 	c.mu.RLock()
 	defer c.mu.RUnlock()
-	b, ok := c.data[questID]
+	b, ok := c.data[k]
 	if !ok {
 		return nil, false
 	}
-	if time.Now().After(c.expiry[questID]) {
+	if time.Now().After(c.expiry[k]) {
 		return nil, false
 	}
 	return b, true
 }
 
-// Put stores quest data in the cache with the configured TTL.
-func (c *QuestCache) Put(questID int, b []byte) {
+// Put stores quest data for the (questID, lang) variant with the configured TTL.
+func (c *QuestCache) Put(questID int, lang string, b []byte) {
+	k := questCacheKey{questID: questID, lang: lang}
 	c.mu.Lock()
-	c.data[questID] = b
-	c.expiry[questID] = time.Now().Add(c.ttl)
+	c.data[k] = b
+	c.expiry[k] = time.Now().Add(c.ttl)
 	c.mu.Unlock()
 }
diff --git a/server/channelserver/quest_cache_test.go b/server/channelserver/quest_cache_test.go
index 1b2d86190..07d63f26b 100644
--- a/server/channelserver/quest_cache_test.go
+++ b/server/channelserver/quest_cache_test.go
@@ -8,7 +8,7 @@ import (
 
 func TestQuestCache_GetMiss(t *testing.T) {
 	c := NewQuestCache(60)
-	_, ok := c.Get(999)
+	_, ok := c.Get(999, "jp")
 	if ok {
 		t.Error("expected cache miss for unknown quest ID")
 	}
@@ -17,9 +17,9 @@ func TestQuestCache_GetMiss(t *testing.T) {
 func TestQuestCache_PutGet(t *testing.T) {
 	c := NewQuestCache(60)
 	data := []byte{0xDE, 0xAD}
-	c.Put(1, data)
+	c.Put(1, "jp", data)
 
-	got, ok := c.Get(1)
+	got, ok := c.Get(1, "jp")
 	if !ok {
 		t.Fatal("expected cache hit")
 	}
@@ -30,9 +30,9 @@ func TestQuestCache_PutGet(t *testing.T) {
 
 func TestQuestCache_Expiry(t *testing.T) {
 	c := NewQuestCache(0) // TTL=0 disables caching
-	c.Put(1, []byte{0x01})
+	c.Put(1, "jp", []byte{0x01})
 
-	_, ok := c.Get(1)
+	_, ok := c.Get(1, "jp")
 	if ok {
 		t.Error("expected cache miss when TTL is 0")
 	}
@@ -40,25 +40,44 @@ func TestQuestCache_Expiry(t *testing.T) {
 
 func TestQuestCache_ExpiryElapsed(t *testing.T) {
 	c := &QuestCache{
-		data:   make(map[int][]byte),
-		expiry: make(map[int]time.Time),
+		data:   make(map[questCacheKey][]byte),
+		expiry: make(map[questCacheKey]time.Time),
 		ttl:    50 * time.Millisecond,
 	}
-	c.Put(1, []byte{0x01})
+	c.Put(1, "jp", []byte{0x01})
 
 	// Should hit immediately
-	if _, ok := c.Get(1); !ok {
+	if _, ok := c.Get(1, "jp"); !ok {
 		t.Fatal("expected cache hit before expiry")
 	}
 
 	time.Sleep(60 * time.Millisecond)
 
 	// Should miss after expiry
-	if _, ok := c.Get(1); ok {
+	if _, ok := c.Get(1, "jp"); ok {
 		t.Error("expected cache miss after expiry")
 	}
 }
 
+// TestQuestCache_LangIsolation verifies that entries for different languages
+// of the same quest ID are stored independently (phase B of #188).
+func TestQuestCache_LangIsolation(t *testing.T) {
+	c := NewQuestCache(60)
+	c.Put(1, "jp", []byte{0x01})
+	c.Put(1, "en", []byte{0x02})
+
+	if got, ok := c.Get(1, "jp"); !ok || got[0] != 0x01 {
+		t.Errorf("jp variant: got %v ok=%v, want [0x01] true", got, ok)
+	}
+	if got, ok := c.Get(1, "en"); !ok || got[0] != 0x02 {
+		t.Errorf("en variant: got %v ok=%v, want [0x02] true", got, ok)
+	}
+	// Unset language variant should miss.
+	if _, ok := c.Get(1, "fr"); ok {
+		t.Error("fr variant should miss when not populated")
+	}
+}
+
 func TestQuestCache_ConcurrentAccess(t *testing.T) {
 	c := NewQuestCache(60)
 	var wg sync.WaitGroup
@@ -67,11 +86,11 @@ func TestQuestCache_ConcurrentAccess(t *testing.T) {
 		id := i
 		go func() {
 			defer wg.Done()
-			c.Put(id, []byte{byte(id)})
+			c.Put(id, "jp", []byte{byte(id)})
 		}()
 		go func() {
 			defer wg.Done()
-			c.Get(id)
+			c.Get(id, "jp")
 		}()
 	}
 	wg.Wait()
diff --git a/server/channelserver/quest_json.go b/server/channelserver/quest_json.go
index 1814cfe3f..10359766b 100644
--- a/server/channelserver/quest_json.go
+++ b/server/channelserver/quest_json.go
@@ -210,15 +210,24 @@ type QuestJSON struct {
 	// Quest identification
 	QuestID uint16 `json:"quest_id"`
 
-	// Text (UTF-8; converted to Shift-JIS in binary)
-	Title       string `json:"title"`
-	Description string `json:"description"`
-	TextMain    string `json:"text_main"`
-	TextSubA    string `json:"text_sub_a"`
-	TextSubB    string `json:"text_sub_b"`
-	SuccessCond string `json:"success_cond"`
-	FailCond    string `json:"fail_cond"`
-	Contractor  string `json:"contractor"`
+	// Text (UTF-8; converted to Shift-JIS in binary).
+	//
+	// Each field accepts either a plain JSON string (single-language, treated
+	// as the value for every language) or a language-keyed object:
+	//
+	//	"title": "リオレウス"
+	//	"title": { "jp": "リオレウス", "en": "Rathalos", "fr": "Rathalos" }
+	//
+	// CompileQuestJSON resolves these based on the compiling session's
+	// language preference (see #188 phase B).
+	Title       LocalizedString `json:"title"`
+	Description LocalizedString `json:"description"`
+	TextMain    LocalizedString `json:"text_main"`
+	TextSubA    LocalizedString `json:"text_sub_a"`
+	TextSubB    LocalizedString `json:"text_sub_b"`
+	SuccessCond LocalizedString `json:"success_cond"`
+	FailCond    LocalizedString `json:"fail_cond"`
+	Contractor  LocalizedString `json:"contractor"`
 
 	// General quest properties (generalQuestProperties section, 0x44–0x85)
 	MonsterSizeMulti uint16 `json:"monster_size_multi"` // 100 = 100%
@@ -421,7 +430,7 @@ func objectiveBytes(obj QuestObjectiveJSON) ([]byte, error) {
 //	             map sections, area mappings, area transitions,
 //	             map info, gathering points, area facilities,
 //	             some strings, gathering tables
-func CompileQuestJSON(data []byte) ([]byte, error) {
+func CompileQuestJSON(data []byte, lang string) ([]byte, error) {
 	var q QuestJSON
 	if err := json.Unmarshal(data, &q); err != nil {
 		return nil, fmt.Errorf("parse quest JSON: %w", err)
@@ -454,10 +463,14 @@ func CompileQuestJSON(data []byte) ([]byte, error) {
 
 	// ── Build Shift-JIS strings ─────────────────────────────────────────
 	// Order matches QuestText struct: title, textMain, textSubA, textSubB,
-	// successCond, failCond, contractor, description.
+	// successCond, failCond, contractor, description. Each LocalizedString
+	// is resolved against the requesting session's language — plain-string
+	// JSON fields resolve to their literal value for every language.
 	rawTexts := []string{
-		q.Title, q.TextMain, q.TextSubA, q.TextSubB,
-		q.SuccessCond, q.FailCond, q.Contractor, q.Description,
+		q.Title.Resolve(lang), q.TextMain.Resolve(lang),
+		q.TextSubA.Resolve(lang), q.TextSubB.Resolve(lang),
+		q.SuccessCond.Resolve(lang), q.FailCond.Resolve(lang),
+		q.Contractor.Resolve(lang), q.Description.Resolve(lang),
 	}
 	var sjisStrings [][]byte
 	for _, s := range rawTexts {
diff --git a/server/channelserver/quest_json_parser.go b/server/channelserver/quest_json_parser.go
index b91a1efc6..d118134f1 100644
--- a/server/channelserver/quest_json_parser.go
+++ b/server/channelserver/quest_json_parser.go
@@ -171,14 +171,17 @@ func ParseQuestBinary(data []byte) (*QuestJSON, error) {
 			}
 			texts[i] = s
 		}
-		q.Title = texts[0]
-		q.TextMain = texts[1]
-		q.TextSubA = texts[2]
-		q.TextSubB = texts[3]
-		q.SuccessCond = texts[4]
-		q.FailCond = texts[5]
-		q.Contractor = texts[6]
-		q.Description = texts[7]
+		// The binary carries only one language, so the reverse path emits
+		// plain-string LocalizedStrings. Editors wanting multi-language
+		// quests should wrap these as {"jp": "...", "en": "..."} by hand.
+		q.Title = NewLocalizedPlain(texts[0])
+		q.TextMain = NewLocalizedPlain(texts[1])
+		q.TextSubA = NewLocalizedPlain(texts[2])
+		q.TextSubB = NewLocalizedPlain(texts[3])
+		q.SuccessCond = NewLocalizedPlain(texts[4])
+		q.FailCond = NewLocalizedPlain(texts[5])
+		q.Contractor = NewLocalizedPlain(texts[6])
+		q.Description = NewLocalizedPlain(texts[7])
 	}
 
 	// ── Stages ───────────────────────────────────────────────────────────
diff --git a/server/channelserver/quest_json_test.go b/server/channelserver/quest_json_test.go
index cf0ff89bf..d592f5d9d 100644
--- a/server/channelserver/quest_json_test.go
+++ b/server/channelserver/quest_json_test.go
@@ -6,6 +6,9 @@ import (
 	"encoding/json"
 	"math"
 	"testing"
+
+	"golang.org/x/text/encoding/japanese"
+	"golang.org/x/text/transform"
 )
 
 // minimalQuestJSON is a small but complete quest used across many test cases.
@@ -57,7 +60,7 @@ var minimalQuestJSON = `{
 // ── Compiler tests (existing) ────────────────────────────────────────────────
 
 func TestCompileQuestJSON_MinimalQuest(t *testing.T) {
-	data, err := CompileQuestJSON([]byte(minimalQuestJSON))
+	data, err := CompileQuestJSON([]byte(minimalQuestJSON), "")
 	if err != nil {
 		t.Fatalf("CompileQuestJSON: %v", err)
 	}
@@ -114,7 +117,7 @@ func TestCompileQuestJSON_BadObjectiveType(t *testing.T) {
 	q.ObjectiveMain.Type = "invalid_type"
 	b, _ := json.Marshal(q)
 
-	_, err := CompileQuestJSON(b)
+	_, err := CompileQuestJSON(b, "")
 	if err == nil {
 		t.Fatal("expected error for invalid objective type, got nil")
 	}
@@ -131,7 +134,7 @@ func TestCompileQuestJSON_AllObjectiveTypes(t *testing.T) {
 			_ = json.Unmarshal([]byte(minimalQuestJSON), &q)
 			q.ObjectiveMain.Type = typ
 			b, _ := json.Marshal(q)
-			if _, err := CompileQuestJSON(b); err != nil {
+			if _, err := CompileQuestJSON(b, ""); err != nil {
 				t.Fatalf("CompileQuestJSON with type %q: %v", typ, err)
 			}
 		})
@@ -143,7 +146,7 @@ func TestCompileQuestJSON_EmptyRewards(t *testing.T) {
 	_ = json.Unmarshal([]byte(minimalQuestJSON), &q)
 	q.Rewards = nil
 	b, _ := json.Marshal(q)
-	if _, err := CompileQuestJSON(b); err != nil {
+	if _, err := CompileQuestJSON(b, ""); err != nil {
 		t.Fatalf("unexpected error with no rewards: %v", err)
 	}
 }
@@ -156,7 +159,7 @@ func TestCompileQuestJSON_MultipleRewardTables(t *testing.T) {
 		{TableID: 2, Items: []QuestRewardItemJSON{{Rate: 100, Item: 153, Quantity: 2}}},
 	}
 	b, _ := json.Marshal(q)
-	data, err := CompileQuestJSON(b)
+	data, err := CompileQuestJSON(b, "")
 	if err != nil {
 		t.Fatalf("CompileQuestJSON: %v", err)
 	}
@@ -189,7 +192,7 @@ func TestParseQuestBinary_NullQuestTypeFlagsPtr(t *testing.T) {
 }
 
 func TestParseQuestBinary_MinimalQuest(t *testing.T) {
-	data, err := CompileQuestJSON([]byte(minimalQuestJSON))
+	data, err := CompileQuestJSON([]byte(minimalQuestJSON), "")
 	if err != nil {
 		t.Fatalf("compile: %v", err)
 	}
@@ -204,24 +207,25 @@ func TestParseQuestBinary_MinimalQuest(t *testing.T) {
 		t.Errorf("QuestID = %d, want 1", q.QuestID)
 	}
 
-	// Text strings
-	if q.Title != "Test Quest" {
-		t.Errorf("Title = %q, want %q", q.Title, "Test Quest")
+	// Text strings — Resolve against empty lang so plain-string JSON fields
+	// return their literal value (phase B of #188).
+	if got := q.Title.Resolve(""); got != "Test Quest" {
+		t.Errorf("Title = %q, want %q", got, "Test Quest")
 	}
-	if q.Description != "A test quest." {
-		t.Errorf("Description = %q, want %q", q.Description, "A test quest.")
+	if got := q.Description.Resolve(""); got != "A test quest." {
+		t.Errorf("Description = %q, want %q", got, "A test quest.")
 	}
-	if q.TextMain != "Hunt the Rathalos." {
-		t.Errorf("TextMain = %q, want %q", q.TextMain, "Hunt the Rathalos.")
+	if got := q.TextMain.Resolve(""); got != "Hunt the Rathalos." {
+		t.Errorf("TextMain = %q, want %q", got, "Hunt the Rathalos.")
 	}
-	if q.SuccessCond != "Slay the Rathalos." {
-		t.Errorf("SuccessCond = %q, want %q", q.SuccessCond, "Slay the Rathalos.")
+	if got := q.SuccessCond.Resolve(""); got != "Slay the Rathalos." {
+		t.Errorf("SuccessCond = %q, want %q", got, "Slay the Rathalos.")
 	}
-	if q.FailCond != "Time runs out or all hunters faint." {
-		t.Errorf("FailCond = %q, want %q", q.FailCond, "Time runs out or all hunters faint.")
+	if got := q.FailCond.Resolve(""); got != "Time runs out or all hunters faint." {
+		t.Errorf("FailCond = %q, want %q", got, "Time runs out or all hunters faint.")
 	}
-	if q.Contractor != "Guild Master" {
-		t.Errorf("Contractor = %q, want %q", q.Contractor, "Guild Master")
+	if got := q.Contractor.Resolve(""); got != "Guild Master" {
+		t.Errorf("Contractor = %q, want %q", got, "Guild Master")
 	}
 
 	// Numeric fields
@@ -348,7 +352,7 @@ func TestParseQuestBinary_MinimalQuest(t *testing.T) {
 func roundTrip(t *testing.T, label, jsonSrc string) {
 	t.Helper()
 
-	bin1, err := CompileQuestJSON([]byte(jsonSrc))
+	bin1, err := CompileQuestJSON([]byte(jsonSrc), "")
 	if err != nil {
 		t.Fatalf("%s: compile(1): %v", label, err)
 	}
@@ -363,7 +367,7 @@ func roundTrip(t *testing.T, label, jsonSrc string) {
 		t.Fatalf("%s: marshal: %v", label, err)
 	}
 
-	bin2, err := CompileQuestJSON(jsonOut)
+	bin2, err := CompileQuestJSON(jsonOut, "")
 	if err != nil {
 		t.Fatalf("%s: compile(2): %v", label, err)
 	}
@@ -773,7 +777,7 @@ func TestRoundTrip_AllSections(t *testing.T) {
 //	mainPropOffset  = 0x86 (= headerSize + genPropSize)
 //	questStringsPtr = 0x1C6 (= mainPropOffset + 320)
 func TestGolden_MinimalQuestBinaryLayout(t *testing.T) {
-	data, err := CompileQuestJSON([]byte(minimalQuestJSON))
+	data, err := CompileQuestJSON([]byte(minimalQuestJSON), "")
 	if err != nil {
 		t.Fatalf("compile: %v", err)
 	}
@@ -981,7 +985,7 @@ func TestGolden_GeneralQuestPropertiesCounts(t *testing.T) {
 	}
 
 	b, _ := json.Marshal(q)
-	data, err := CompileQuestJSON(b)
+	data, err := CompileQuestJSON(b, "")
 	if err != nil {
 		t.Fatalf("compile: %v", err)
 	}
@@ -1007,7 +1011,7 @@ func TestGolden_MapSectionsBinaryLayout(t *testing.T) {
 		},
 	}
 
-	data, err := CompileQuestJSON(func() []byte { b, _ := json.Marshal(q); return b }())
+	data, err := CompileQuestJSON(func() []byte { b, _ := json.Marshal(q); return b }(), "")
 	if err != nil {
 		t.Fatalf("compile: %v", err)
 	}
@@ -1097,7 +1101,7 @@ func TestGolden_GatheringTablesBinaryLayout(t *testing.T) {
 	}
 
 	b, _ := json.Marshal(q)
-	data, err := CompileQuestJSON(b)
+	data, err := CompileQuestJSON(b, "")
 	if err != nil {
 		t.Fatalf("compile: %v", err)
 	}
@@ -1263,3 +1267,127 @@ func assertF32(t *testing.T, data []byte, off int, want float32, label string) {
 		t.Errorf("%s @ 0x%X: got %v, want %v", label, off, got, want)
 	}
 }
+
+// ── Phase B: localized quest text (#188) ─────────────────────────────────────
+
+// localizedQuestJSON exercises the LocalizedString schema — title is a map,
+// description is a mixed map, and the rest fall back to plain strings so the
+// test also covers the "most fields stay plain" migration path.
+var localizedQuestJSON = `{
+	"quest_id": 1,
+	"title": { "jp": "テストクエスト", "en": "Test Quest EN", "fr": "Test Quest FR" },
+	"description": { "jp": "説明", "en": "A test quest." },
+	"text_main": "Hunt the Rathalos.",
+	"text_sub_a": "",
+	"text_sub_b": "",
+	"success_cond": "Slay the Rathalos.",
+	"fail_cond": "Time runs out or all hunters faint.",
+	"contractor": "Guild Master",
+	"monster_size_multi": 100,
+	"main_rank_points": 120,
+	"sub_a_rank_points": 60,
+	"sub_b_rank_points": 0,
+	"fee": 500,
+	"reward_main": 5000,
+	"reward_sub_a": 1000,
+	"reward_sub_b": 0,
+	"time_limit_minutes": 50,
+	"map": 2,
+	"rank_band": 0,
+	"objective_main": {"type": "hunt", "target": 11, "count": 1},
+	"objective_sub_a": {"type": "deliver", "target": 149, "count": 3},
+	"objective_sub_b": {"type": "none"},
+	"large_monsters": [
+		{"id": 11, "spawn_amount": 1, "spawn_stage": 5, "orientation": 180, "x": 1500.0, "y": 0.0, "z": -2000.0}
+	],
+	"rewards": [
+		{"table_id": 1, "items": [{"rate": 50, "item": 149, "quantity": 1}]}
+	],
+	"supply_main": [{"item": 1, "quantity": 5}],
+	"stages": [{"stage_id": 2}]
+}`
+
+// extractQuestTitle reads the first Shift-JIS null-terminated string pointed
+// to by the QuestText pointer table and decodes it back to UTF-8. This lets
+// the test verify which language variant the compiler selected without
+// replicating the full binary layout.
+func extractQuestTitle(t *testing.T, data []byte) string {
+	t.Helper()
+	// Header offset 0x00 is the first pointer = questTypeFlagsPtr = 0x86.
+	// QuestStringsTablePtr is at headerSize + genPropSize + mainPropSize.
+	const questStringsTableOff = 68 + 66 + questBodyLenZZ // 0x1C6
+	if questStringsTableOff+4 > len(data) {
+		t.Fatalf("data too short for quest strings table: %d", len(data))
+	}
+	// First 4 bytes of the strings table point to the title string.
+	titlePtr := binary.LittleEndian.Uint32(data[questStringsTableOff:])
+	if int(titlePtr) >= len(data) {
+		t.Fatalf("title pointer 0x%X out of range (len=%d)", titlePtr, len(data))
+	}
+	end := int(titlePtr)
+	for end < len(data) && data[end] != 0 {
+		end++
+	}
+	sjis := data[titlePtr:end]
+	decoded, _, err := transform.Bytes(japanese.ShiftJIS.NewDecoder(), sjis)
+	if err != nil {
+		t.Fatalf("decode title: %v", err)
+	}
+	return string(decoded)
+}
+
+func TestCompileQuestJSON_LocalizedTitle_JapanesePicked(t *testing.T) {
+	data, err := CompileQuestJSON([]byte(localizedQuestJSON), "jp")
+	if err != nil {
+		t.Fatalf("CompileQuestJSON: %v", err)
+	}
+	if got := extractQuestTitle(t, data); got != "テストクエスト" {
+		t.Errorf("jp title = %q, want %q", got, "テストクエスト")
+	}
+}
+
+func TestCompileQuestJSON_LocalizedTitle_EnglishPicked(t *testing.T) {
+	data, err := CompileQuestJSON([]byte(localizedQuestJSON), "en")
+	if err != nil {
+		t.Fatalf("CompileQuestJSON: %v", err)
+	}
+	if got := extractQuestTitle(t, data); got != "Test Quest EN" {
+		t.Errorf("en title = %q, want %q", got, "Test Quest EN")
+	}
+}
+
+func TestCompileQuestJSON_LocalizedTitle_FrenchPicked(t *testing.T) {
+	data, err := CompileQuestJSON([]byte(localizedQuestJSON), "fr")
+	if err != nil {
+		t.Fatalf("CompileQuestJSON: %v", err)
+	}
+	if got := extractQuestTitle(t, data); got != "Test Quest FR" {
+		t.Errorf("fr title = %q, want %q", got, "Test Quest FR")
+	}
+}
+
+// Phase B fallback: Spanish is not provided in localizedQuestJSON, so the
+// compiler should fall back to the canonical jp variant.
+func TestCompileQuestJSON_LocalizedTitle_MissingLangFallsBackToJP(t *testing.T) {
+	data, err := CompileQuestJSON([]byte(localizedQuestJSON), "es")
+	if err != nil {
+		t.Fatalf("CompileQuestJSON: %v", err)
+	}
+	if got := extractQuestTitle(t, data); got != "テストクエスト" {
+		t.Errorf("es fallback title = %q, want jp %q", got, "テストクエスト")
+	}
+}
+
+// Phase B backwards-compat: existing plain-string quest JSON must produce
+// the exact same title regardless of requested language.
+func TestCompileQuestJSON_PlainString_SameAcrossLanguages(t *testing.T) {
+	for _, lang := range []string{"", "jp", "en", "fr", "es"} {
+		data, err := CompileQuestJSON([]byte(minimalQuestJSON), lang)
+		if err != nil {
+			t.Fatalf("lang=%q: CompileQuestJSON: %v", lang, err)
+		}
+		if got := extractQuestTitle(t, data); got != "Test Quest" {
+			t.Errorf("lang=%q: title = %q, want %q", lang, got, "Test Quest")
+		}
+	}
+}