diff --git a/CHANGELOG.md b/CHANGELOG.md
index 964512cbc..6280c64b9 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
 
+- Per-session i18n routing and localized scenarios (phase C of [#188](https://github.com/Mezeporta/Erupe/issues/188)): `Session.I18n()` returns a cached, language-resolved `i18n` table built via `getLangStringsFor(s.Lang())`; `SetLang` invalidates the cache. All 51 existing `s.server.i18n.*` call sites in `handlers_commands.go`, `handlers_guild.go`, `handlers_guild_scout.go`, `handlers_cafe.go`, and `handlers_cast_binary.go` now route through `s.I18n().*`, so chat replies, guild invite mails, cafe reset notices, and quest-timer broadcasts are served in the player's preferred language. Scenario JSON subheader `strings` and inline entry `text` fields now accept the same plain/map `LocalizedString` schema as quests (phase B); `CompileScenarioJSON` takes a language argument and `loadScenarioBinary` passes `s.Lang()`. Round-tripping existing `.bin` files through the JSON path still produces byte-identical output. World-wide broadcasts (Raviente siege announcements via `BroadcastRaviente`) intentionally remain on the server default because they have no single-session context.
 - 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.
 
diff --git a/server/channelserver/handlers_cafe.go b/server/channelserver/handlers_cafe.go
index c7983c421..08918654f 100644
--- a/server/channelserver/handlers_cafe.go
+++ b/server/channelserver/handlers_cafe.go
@@ -103,7 +103,7 @@ func handleMsgMhfGetCafeDuration(s *Session, p mhfpacket.MHFPacket) {
 	bf.WriteUint32(uint32(cafeTime))
 	if s.server.erupeConfig.RealClientMode >= cfg.ZZ {
 		bf.WriteUint16(0)
-		ps.Uint16(bf, fmt.Sprintf(s.server.i18n.cafe.reset, int(cafeReset.Month()), cafeReset.Day()), true)
+		ps.Uint16(bf, fmt.Sprintf(s.I18n().cafe.reset, int(cafeReset.Month()), cafeReset.Day()), true)
 	}
 	doAckBufSucceed(s, pkt.AckHandle, bf.Data())
 }
diff --git a/server/channelserver/handlers_cast_binary.go b/server/channelserver/handlers_cast_binary.go
index 3ea575a0f..380c93232 100644
--- a/server/channelserver/handlers_cast_binary.go
+++ b/server/channelserver/handlers_cast_binary.go
@@ -49,7 +49,7 @@ func handleMsgSysCastBinary(s *Session, p mhfpacket.MHFPacket) {
 				_ = tmp.ReadBytes(9)
 				tmp.SetLE()
 				frame := tmp.ReadUint32()
-				sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.timer, frame/30/60/60, frame/30/60, frame/30%60, int(math.Round(float64(frame%30*100)/3)), frame))
+				sendServerChatMessage(s, fmt.Sprintf(s.I18n().timer, frame/30/60/60, frame/30/60, frame/30%60, int(math.Round(float64(frame%30*100)/3)), frame))
 			}
 		}
 	}
diff --git a/server/channelserver/handlers_commands.go b/server/channelserver/handlers_commands.go
index 6d70d051f..2dd08bd66 100644
--- a/server/channelserver/handlers_commands.go
+++ b/server/channelserver/handlers_commands.go
@@ -41,7 +41,7 @@ func initCommands(cmds []cfg.Command, logger *zap.Logger) {
 }
 
 func sendDisabledCommandMessage(s *Session, cmd cfg.Command) {
-	sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.disabled, cmd.Name))
+	sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.disabled, cmd.Name))
 }
 
 const chatFlagServer = 0x80 // marks a message as server-originated
@@ -95,7 +95,7 @@ func parseChatCommand(s *Session, command string) {
 							expiry = time.Now().Add(time.Duration(length) * time.Hour * 24 * 365)
 						}
 					} else {
-						sendServerChatMessage(s, s.server.i18n.commands.ban.error)
+						sendServerChatMessage(s, s.I18n().commands.ban.error)
 						return
 					}
 				}
@@ -107,25 +107,25 @@ func parseChatCommand(s *Session, command string) {
 							if err := s.server.userRepo.BanUser(uid, nil); err != nil {
 								s.logger.Error("Failed to ban user", zap.Error(err))
 							}
-							sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.ban.success, uname))
+							sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.ban.success, uname))
 						} else {
 							if err := s.server.userRepo.BanUser(uid, &expiry); err != nil {
 								s.logger.Error("Failed to ban user with expiry", zap.Error(err))
 							}
-							sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.ban.success, uname)+fmt.Sprintf(s.server.i18n.commands.ban.length, expiry.Format(time.DateTime)))
+							sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.ban.success, uname)+fmt.Sprintf(s.I18n().commands.ban.length, expiry.Format(time.DateTime)))
 						}
 						s.server.DisconnectUser(uid)
 					} else {
-						sendServerChatMessage(s, s.server.i18n.commands.ban.noUser)
+						sendServerChatMessage(s, s.I18n().commands.ban.noUser)
 					}
 				} else {
-					sendServerChatMessage(s, s.server.i18n.commands.ban.invalid)
+					sendServerChatMessage(s, s.I18n().commands.ban.invalid)
 				}
 			} else {
-				sendServerChatMessage(s, s.server.i18n.commands.ban.error)
+				sendServerChatMessage(s, s.I18n().commands.ban.error)
 			}
 		} else {
-			sendServerChatMessage(s, s.server.i18n.commands.noOp)
+			sendServerChatMessage(s, s.I18n().commands.noOp)
 		}
 	case commands["Timer"].Prefix:
 		if commands["Timer"].Enabled || s.isOp() {
@@ -137,9 +137,9 @@ func parseChatCommand(s *Session, command string) {
 				s.logger.Error("Failed to update timer setting", zap.Error(err))
 			}
 			if state {
-				sendServerChatMessage(s, s.server.i18n.commands.timer.disabled)
+				sendServerChatMessage(s, s.I18n().commands.timer.disabled)
 			} else {
-				sendServerChatMessage(s, s.server.i18n.commands.timer.enabled)
+				sendServerChatMessage(s, s.I18n().commands.timer.enabled)
 			}
 		} else {
 			sendDisabledCommandMessage(s, commands["Timer"])
@@ -181,20 +181,20 @@ func parseChatCommand(s *Session, command string) {
 				if exists == 0 {
 					err := s.server.userRepo.SetPSNID(s.userID, args[1])
 					if err == nil {
-						sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.psn.success, args[1]))
+						sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.psn.success, args[1]))
 					}
 				} else {
-					sendServerChatMessage(s, s.server.i18n.commands.psn.exists)
+					sendServerChatMessage(s, s.I18n().commands.psn.exists)
 				}
 			} else {
-				sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.psn.error, commands["PSN"].Prefix))
+				sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.psn.error, commands["PSN"].Prefix))
 			}
 		} else {
 			sendDisabledCommandMessage(s, commands["PSN"])
 		}
 	case commands["Reload"].Prefix:
 		if commands["Reload"].Enabled || s.isOp() {
-			sendServerChatMessage(s, s.server.i18n.commands.reload)
+			sendServerChatMessage(s, s.I18n().commands.reload)
 			var temp mhfpacket.MHFPacket
 			deleteNotif := byteframe.NewByteFrame()
 			for _, object := range s.stage.objects {
@@ -256,24 +256,24 @@ func parseChatCommand(s *Session, command string) {
 	case commands["KeyQuest"].Prefix:
 		if commands["KeyQuest"].Enabled || s.isOp() {
 			if s.server.erupeConfig.RealClientMode < cfg.G10 {
-				sendServerChatMessage(s, s.server.i18n.commands.kqf.version)
+				sendServerChatMessage(s, s.I18n().commands.kqf.version)
 			} else {
 				if len(args) > 1 {
 					switch args[1] {
 					case "get":
-						sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.kqf.get, s.kqf))
+						sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.kqf.get, s.kqf))
 					case "set":
 						if len(args) > 2 && len(args[2]) == 16 {
 							hexd, err := hex.DecodeString(args[2])
 							if err != nil {
-								sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.kqf.set.error, commands["KeyQuest"].Prefix))
+								sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.kqf.set.error, commands["KeyQuest"].Prefix))
 								return
 							}
 							s.kqf = hexd
 							s.kqfOverride = true
-							sendServerChatMessage(s, s.server.i18n.commands.kqf.set.success)
+							sendServerChatMessage(s, s.I18n().commands.kqf.set.success)
 						} else {
-							sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.kqf.set.error, commands["KeyQuest"].Prefix))
+							sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.kqf.set.error, commands["KeyQuest"].Prefix))
 						}
 					}
 				}
@@ -286,17 +286,17 @@ func parseChatCommand(s *Session, command string) {
 			if len(args) > 1 {
 				v, err := strconv.Atoi(args[1])
 				if err != nil || v < 0 || v > math.MaxUint32 {
-					sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.rights.error, commands["Rights"].Prefix))
+					sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.rights.error, commands["Rights"].Prefix))
 					return
 				}
 				err = s.server.userRepo.SetRights(s.userID, uint32(v))
 				if err == nil {
-					sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.rights.success, v))
+					sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.rights.success, v))
 				} else {
-					sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.rights.error, commands["Rights"].Prefix))
+					sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.rights.error, commands["Rights"].Prefix))
 				}
 			} else {
-				sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.rights.error, commands["Rights"].Prefix))
+				sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.rights.error, commands["Rights"].Prefix))
 			}
 		} else {
 			sendDisabledCommandMessage(s, commands["Rights"])
@@ -320,11 +320,11 @@ func parseChatCommand(s *Session, command string) {
 									})
 									if ei != -1 {
 										delta = uint32(-1 * math.Pow(2, float64(course.ID)))
-										sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.course.disabled, course.Aliases()[0]))
+										sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.course.disabled, course.Aliases()[0]))
 									}
 								} else {
 									delta = uint32(math.Pow(2, float64(course.ID)))
-									sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.course.enabled, course.Aliases()[0]))
+									sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.course.enabled, course.Aliases()[0]))
 								}
 								rightsInt, err := s.server.userRepo.GetRights(s.userID)
 								if err == nil {
@@ -334,14 +334,14 @@ func parseChatCommand(s *Session, command string) {
 								}
 								updateRights(s)
 							} else {
-								sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.course.locked, course.Aliases()[0]))
+								sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.course.locked, course.Aliases()[0]))
 							}
 							return
 						}
 					}
 				}
 			} else {
-				sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.course.error, commands["Course"].Prefix))
+				sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.course.error, commands["Course"].Prefix))
 			}
 		} else {
 			sendDisabledCommandMessage(s, commands["Course"])
@@ -354,45 +354,45 @@ func parseChatCommand(s *Session, command string) {
 					case "start":
 						if s.server.raviente.register[1] == 0 {
 							s.server.raviente.register[1] = s.server.raviente.register[3]
-							sendServerChatMessage(s, s.server.i18n.commands.ravi.start.success)
+							sendServerChatMessage(s, s.I18n().commands.ravi.start.success)
 							s.notifyRavi()
 						} else {
-							sendServerChatMessage(s, s.server.i18n.commands.ravi.start.error)
+							sendServerChatMessage(s, s.I18n().commands.ravi.start.error)
 						}
 					case "cm", "check", "checkmultiplier", "multiplier":
-						sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.ravi.multiplier, s.server.GetRaviMultiplier()))
+						sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.ravi.multiplier, s.server.GetRaviMultiplier()))
 					case "sr", "sendres", "resurrection", "ss", "sendsed", "rs", "reqsed":
 						if s.server.erupeConfig.RealClientMode == cfg.ZZ {
 							switch args[1] {
 							case "sr", "sendres", "resurrection":
 								if s.server.raviente.state[28] > 0 {
-									sendServerChatMessage(s, s.server.i18n.commands.ravi.res.success)
+									sendServerChatMessage(s, s.I18n().commands.ravi.res.success)
 									s.server.raviente.state[28] = 0
 								} else {
-									sendServerChatMessage(s, s.server.i18n.commands.ravi.res.error)
+									sendServerChatMessage(s, s.I18n().commands.ravi.res.error)
 								}
 							case "ss", "sendsed":
-								sendServerChatMessage(s, s.server.i18n.commands.ravi.sed.success)
+								sendServerChatMessage(s, s.I18n().commands.ravi.sed.success)
 								// Total BerRavi HP
 								HP := s.server.raviente.state[0] + s.server.raviente.state[1] + s.server.raviente.state[2] + s.server.raviente.state[3] + s.server.raviente.state[4]
 								s.server.raviente.support[1] = HP
 							case "rs", "reqsed":
-								sendServerChatMessage(s, s.server.i18n.commands.ravi.request)
+								sendServerChatMessage(s, s.I18n().commands.ravi.request)
 								// Total BerRavi HP
 								HP := s.server.raviente.state[0] + s.server.raviente.state[1] + s.server.raviente.state[2] + s.server.raviente.state[3] + s.server.raviente.state[4]
 								s.server.raviente.support[1] = HP + 1
 							}
 						} else {
-							sendServerChatMessage(s, s.server.i18n.commands.ravi.version)
+							sendServerChatMessage(s, s.I18n().commands.ravi.version)
 						}
 					default:
-						sendServerChatMessage(s, s.server.i18n.commands.ravi.error)
+						sendServerChatMessage(s, s.I18n().commands.ravi.error)
 					}
 				} else {
-					sendServerChatMessage(s, s.server.i18n.commands.ravi.noPlayers)
+					sendServerChatMessage(s, s.I18n().commands.ravi.noPlayers)
 				}
 			} else {
-				sendServerChatMessage(s, s.server.i18n.commands.ravi.error)
+				sendServerChatMessage(s, s.I18n().commands.ravi.error)
 			}
 		} else {
 			sendDisabledCommandMessage(s, commands["Raviente"])
@@ -402,12 +402,12 @@ func parseChatCommand(s *Session, command string) {
 			if len(args) > 2 {
 				x, err := strconv.ParseInt(args[1], 10, 16)
 				if err != nil {
-					sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.teleport.error, commands["Teleport"].Prefix))
+					sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.teleport.error, commands["Teleport"].Prefix))
 					return
 				}
 				y, err := strconv.ParseInt(args[2], 10, 16)
 				if err != nil {
-					sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.teleport.error, commands["Teleport"].Prefix))
+					sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.teleport.error, commands["Teleport"].Prefix))
 					return
 				}
 				payload := byteframe.NewByteFrame()
@@ -421,9 +421,9 @@ func parseChatCommand(s *Session, command string) {
 					MessageType:    BinaryMessageTypeState,
 					RawDataPayload: payloadBytes,
 				})
-				sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.teleport.success, x, y))
+				sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.teleport.success, x, y))
 			} else {
-				sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.teleport.error, commands["Teleport"].Prefix))
+				sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.teleport.error, commands["Teleport"].Prefix))
 			}
 		} else {
 			sendDisabledCommandMessage(s, commands["Teleport"])
@@ -439,14 +439,14 @@ func parseChatCommand(s *Session, command string) {
 					s.logger.Error("Failed to update discord token", zap.Error(err))
 				}
 			}
-			sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.discord.success, _token))
+			sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.discord.success, _token))
 		} else {
 			sendDisabledCommandMessage(s, commands["Discord"])
 		}
 	case commands["Playtime"].Prefix:
 		if commands["Playtime"].Enabled || s.isOp() {
 			playtime := s.playtime + uint32(time.Since(s.playtimeTime).Seconds())
-			sendServerChatMessage(s, fmt.Sprintf(s.server.i18n.commands.playtime, playtime/60/60, playtime/60%60, playtime%60))
+			sendServerChatMessage(s, fmt.Sprintf(s.I18n().commands.playtime, playtime/60/60, playtime/60%60, playtime%60))
 		} else {
 			sendDisabledCommandMessage(s, commands["Playtime"])
 		}
diff --git a/server/channelserver/handlers_guild.go b/server/channelserver/handlers_guild.go
index 0e5b5d132..d9b825b83 100644
--- a/server/channelserver/handlers_guild.go
+++ b/server/channelserver/handlers_guild.go
@@ -376,10 +376,10 @@ func handleMsgMhfEntryRookieGuild(s *Session, p mhfpacket.MHFPacket) {
 	// pkt.Unk==0: fresh rookie entering a rookie guild (return_type=1).
 	// pkt.Unk>=1: returning player entering a comeback/return guild (return_type=2).
 	returnType := uint8(1)
-	nameTemplate := s.server.i18n.guild.rookieGuildName
+	nameTemplate := s.I18n().guild.rookieGuildName
 	if pkt.Unk >= 1 {
 		returnType = 2
-		nameTemplate = s.server.i18n.guild.returnGuildName
+		nameTemplate = s.I18n().guild.returnGuildName
 	}
 
 	guildID, err := s.server.guildRepo.FindOrCreateReturnGuild(returnType, nameTemplate)
diff --git a/server/channelserver/handlers_guild_scout.go b/server/channelserver/handlers_guild_scout.go
index ab5ea8042..b4d81a767 100644
--- a/server/channelserver/handlers_guild_scout.go
+++ b/server/channelserver/handlers_guild_scout.go
@@ -13,8 +13,8 @@ func handleMsgMhfPostGuildScout(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgMhfPostGuildScout)
 
 	err := s.server.guildService.PostScout(s.charID, pkt.CharID, ScoutInviteStrings{
-		Title: s.server.i18n.guild.invite.title,
-		Body:  s.server.i18n.guild.invite.body,
+		Title: s.I18n().guild.invite.title,
+		Body:  s.I18n().guild.invite.body,
 	})
 
 	if errors.Is(err, ErrAlreadyInvited) {
@@ -66,7 +66,7 @@ func handleMsgMhfCancelGuildScout(s *Session, p mhfpacket.MHFPacket) {
 func handleMsgMhfAnswerGuildScout(s *Session, p mhfpacket.MHFPacket) {
 	pkt := p.(*mhfpacket.MsgMhfAnswerGuildScout)
 
-	i := s.server.i18n.guild.invite
+	i := s.I18n().guild.invite
 	result, err := s.server.guildService.AnswerScout(s.charID, pkt.LeaderID, pkt.Answer, AnswerScoutStrings{
 		SuccessTitle:  i.success.title,
 		SuccessBody:   i.success.body,
diff --git a/server/channelserver/handlers_quest.go b/server/channelserver/handlers_quest.go
index 2ac1bd90a..b9bb9af87 100644
--- a/server/channelserver/handlers_quest.go
+++ b/server/channelserver/handlers_quest.go
@@ -181,7 +181,7 @@ func loadScenarioBinary(s *Session, filename string) ([]byte, error) {
 	if err != nil {
 		return nil, err
 	}
-	compiled, err := CompileScenarioJSON(jsonData)
+	compiled, err := CompileScenarioJSON(jsonData, s.Lang())
 	if err != nil {
 		return nil, fmt.Errorf("compile scenario JSON %s: %w", filename, err)
 	}
diff --git a/server/channelserver/scenario_json.go b/server/channelserver/scenario_json.go
index 50d24ee65..5171852d9 100644
--- a/server/channelserver/scenario_json.go
+++ b/server/channelserver/scenario_json.go
@@ -102,16 +102,22 @@ type ScenarioSubheaderJSON struct {
 	// fields, including those the server does not need to interpret.
 	// For chunk0, the client only reads m[0]–m[6]; m[7]–m[9] are ignored.
 	Metadata string `json:"metadata"`
-	// Strings contains the human-editable text (UTF-8).
-	// The compiler converts each string to null-terminated Shift-JIS on the wire.
-	Strings []string `json:"strings"`
+	// Strings contains the human-editable text. Each entry accepts either a
+	// plain UTF-8 string (backwards compatible, single-language) or a
+	// language-keyed object; see LocalizedString. The compiler converts the
+	// resolved value for the current session's language to null-terminated
+	// Shift-JIS on the wire.
+	Strings []LocalizedString `json:"strings"`
 }
 
 // ScenarioInlineEntry is one entry in an inline-format chunk0.
 // Format on wire: {u8 index}{Shift-JIS string}{0x00}.
+//
+// Text accepts either a plain string or a language-keyed object; see
+// LocalizedString.
 type ScenarioInlineEntry struct {
-	Index uint8  `json:"index"`
-	Text  string `json:"text"`
+	Index uint8           `json:"index"`
+	Text  LocalizedString `json:"text"`
 }
 
 // ScenarioRawChunkJSON stores a JKR-compressed chunk as its raw compressed bytes.
@@ -239,17 +245,23 @@ func parseScenarioSubheader(data []byte) (*ScenarioSubheaderJSON, error) {
 
 	metadata := base64.StdEncoding.EncodeToString(data[8:metaEnd])
 
-	strings, err := scenarioReadStrings(data, metaEnd, entryCount)
+	plainStrings, err := scenarioReadStrings(data, metaEnd, entryCount)
 	if err != nil {
 		return nil, err
 	}
+	// Binary carries a single language — wrap as plain LocalizedStrings so
+	// round-tripping emits the same bytes.
+	localized := make([]LocalizedString, len(plainStrings))
+	for i, s := range plainStrings {
+		localized[i] = NewLocalizedPlain(s)
+	}
 
 	return &ScenarioSubheaderJSON{
 		Type:     chunkType,
 		Unknown1: unknown1,
 		Unknown2: unknown2,
 		Metadata: metadata,
-		Strings:  strings,
+		Strings:  localized,
 	}, nil
 }
 
@@ -276,7 +288,7 @@ func parseScenarioInline(data []byte) ([]ScenarioInlineEntry, error) {
 			if err != nil {
 				return nil, fmt.Errorf("inline entry at 0x%x: %w", pos, err)
 			}
-			result = append(result, ScenarioInlineEntry{Index: idx, Text: text})
+			result = append(result, ScenarioInlineEntry{Index: idx, Text: NewLocalizedPlain(text)})
 		}
 		pos = end + 1 // skip null terminator
 	}
@@ -317,27 +329,30 @@ func scenarioReadStrings(data []byte, start, maxCount int) ([]string, error) {
 
 // ── Compile: JSON → binary ───────────────────────────────────────────────────
 
-// CompileScenarioJSON parses jsonData and compiles it to MHF scenario binary format.
-func CompileScenarioJSON(jsonData []byte) ([]byte, error) {
+// CompileScenarioJSON parses jsonData and compiles it to MHF scenario binary
+// format for the given language. Phase B of #188 added the lang parameter so
+// per-session scenarios can ship localized text without affecting callers
+// holding single-language JSON files.
+func CompileScenarioJSON(jsonData []byte, lang string) ([]byte, error) {
 	var s ScenarioJSON
 	if err := json.Unmarshal(jsonData, &s); err != nil {
 		return nil, fmt.Errorf("unmarshal scenario JSON: %w", err)
 	}
-	return compileScenario(&s)
+	return compileScenario(&s, lang)
 }
 
-func compileScenario(s *ScenarioJSON) ([]byte, error) {
+func compileScenario(s *ScenarioJSON, lang string) ([]byte, error) {
 	var chunk0, chunk1, chunk2 []byte
 	var err error
 
 	if s.Chunk0 != nil {
-		chunk0, err = compileScenarioChunk0(s.Chunk0)
+		chunk0, err = compileScenarioChunk0(s.Chunk0, lang)
 		if err != nil {
 			return nil, fmt.Errorf("chunk0: %w", err)
 		}
 	}
 	if s.Chunk1 != nil {
-		chunk1, err = compileScenarioChunk1(s.Chunk1)
+		chunk1, err = compileScenarioChunk1(s.Chunk1, lang)
 		if err != nil {
 			return nil, fmt.Errorf("chunk1: %w", err)
 		}
@@ -370,26 +385,26 @@ func compileScenario(s *ScenarioJSON) ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
-func compileScenarioChunk0(c *ScenarioChunk0JSON) ([]byte, error) {
+func compileScenarioChunk0(c *ScenarioChunk0JSON, lang string) ([]byte, error) {
 	if c.Subheader != nil {
-		return compileScenarioSubheader(c.Subheader)
+		return compileScenarioSubheader(c.Subheader, lang)
 	}
-	return compileScenarioInline(c.Inline)
+	return compileScenarioInline(c.Inline, lang)
 }
 
-func compileScenarioChunk1(c *ScenarioChunk1JSON) ([]byte, error) {
+func compileScenarioChunk1(c *ScenarioChunk1JSON, lang string) ([]byte, error) {
 	if c.JKR != nil {
 		return compileScenarioRawChunk(c.JKR)
 	}
 	if c.Subheader != nil {
-		return compileScenarioSubheader(c.Subheader)
+		return compileScenarioSubheader(c.Subheader, lang)
 	}
 	return nil, nil
 }
 
 // compileScenarioSubheader builds the binary sub-header chunk:
 // [8-byte header][metadata][null-terminated Shift-JIS strings][0xFF]
-func compileScenarioSubheader(sh *ScenarioSubheaderJSON) ([]byte, error) {
+func compileScenarioSubheader(sh *ScenarioSubheaderJSON, lang string) ([]byte, error) {
 	meta, err := base64.StdEncoding.DecodeString(sh.Metadata)
 	if err != nil {
 		return nil, fmt.Errorf("decode metadata base64: %w", err)
@@ -397,7 +412,7 @@ func compileScenarioSubheader(sh *ScenarioSubheaderJSON) ([]byte, error) {
 
 	var strBuf bytes.Buffer
 	for _, s := range sh.Strings {
-		sjis, err := scenarioEncodeShiftJIS(s)
+		sjis, err := scenarioEncodeShiftJIS(s.Resolve(lang))
 		if err != nil {
 			return nil, err
 		}
@@ -425,11 +440,11 @@ func compileScenarioSubheader(sh *ScenarioSubheaderJSON) ([]byte, error) {
 }
 
 // compileScenarioInline builds the inline-format chunk0 bytes.
-func compileScenarioInline(entries []ScenarioInlineEntry) ([]byte, error) {
+func compileScenarioInline(entries []ScenarioInlineEntry, lang string) ([]byte, error) {
 	var buf bytes.Buffer
 	for _, e := range entries {
 		buf.WriteByte(e.Index)
-		sjis, err := scenarioEncodeShiftJIS(e.Text)
+		sjis, err := scenarioEncodeShiftJIS(e.Text.Resolve(lang))
 		if err != nil {
 			return nil, err
 		}
diff --git a/server/channelserver/scenario_json_test.go b/server/channelserver/scenario_json_test.go
index 134a10045..6ef48a1c3 100644
--- a/server/channelserver/scenario_json_test.go
+++ b/server/channelserver/scenario_json_test.go
@@ -85,14 +85,18 @@ func extractStringsFromScenario(t *testing.T, data []byte) []string {
 	var result []string
 	if s.Chunk0 != nil {
 		if s.Chunk0.Subheader != nil {
-			result = append(result, s.Chunk0.Subheader.Strings...)
+			for _, ls := range s.Chunk0.Subheader.Strings {
+				result = append(result, ls.Resolve(""))
+			}
 		}
 		for _, e := range s.Chunk0.Inline {
-			result = append(result, e.Text)
+			result = append(result, e.Text.Resolve(""))
 		}
 	}
 	if s.Chunk1 != nil && s.Chunk1.Subheader != nil {
-		result = append(result, s.Chunk1.Subheader.Strings...)
+		for _, ls := range s.Chunk1.Subheader.Strings {
+			result = append(result, ls.Resolve(""))
+		}
 	}
 	return result
 }
@@ -134,8 +138,8 @@ func TestParseScenarioBinary_SubheaderChunk0(t *testing.T) {
 		t.Fatalf("string count: got %d, want %d", len(got), len(want))
 	}
 	for i := range want {
-		if got[i] != want[i] {
-			t.Errorf("[%d]: got %q, want %q", i, got[i], want[i])
+		if got[i].Resolve("") != want[i] {
+			t.Errorf("[%d]: got %q, want %q", i, got[i].Resolve(""), want[i])
 		}
 	}
 }
@@ -153,8 +157,8 @@ func TestParseScenarioBinary_InlineChunk0(t *testing.T) {
 	}
 	want := []string{"Item1", "Item2"}
 	for i, e := range s.Chunk0.Inline {
-		if e.Text != want[i] {
-			t.Errorf("[%d]: got %q, want %q", i, e.Text, want[i])
+		if got := e.Text.Resolve(""); got != want[i] {
+			t.Errorf("[%d]: got %q, want %q", i, got, want[i])
 		}
 	}
 }
@@ -187,8 +191,8 @@ func TestParseScenarioBinary_Japanese(t *testing.T) {
 	want := []string{"テスト", "日本語"}
 	got := s.Chunk0.Subheader.Strings
 	for i := range want {
-		if got[i] != want[i] {
-			t.Errorf("[%d]: got %q, want %q", i, got[i], want[i])
+		if got[i].Resolve("") != want[i] {
+			t.Errorf("[%d]: got %q, want %q", i, got[i].Resolve(""), want[i])
 		}
 	}
 }
@@ -203,7 +207,7 @@ func TestCompileScenarioJSON_Subheader(t *testing.T) {
 				Unknown1: 0x00,
 				Unknown2: 0x00,
 				Metadata: "AAAABBBB", // base64 of 6 zero bytes
-				Strings:  []string{"Hello", "World"},
+				Strings:  []LocalizedString{NewLocalizedPlain("Hello"), NewLocalizedPlain("World")},
 			},
 		},
 	}
@@ -213,7 +217,7 @@ func TestCompileScenarioJSON_Subheader(t *testing.T) {
 		t.Fatalf("marshal: %v", err)
 	}
 
-	compiled, err := CompileScenarioJSON(jsonData)
+	compiled, err := CompileScenarioJSON(jsonData, "")
 	if err != nil {
 		t.Fatalf("CompileScenarioJSON: %v", err)
 	}
@@ -229,8 +233,8 @@ func TestCompileScenarioJSON_Subheader(t *testing.T) {
 	want := []string{"Hello", "World"}
 	got := result.Chunk0.Subheader.Strings
 	for i := range want {
-		if i >= len(got) || got[i] != want[i] {
-			t.Errorf("[%d]: got %q, want %q", i, got[i], want[i])
+		if i >= len(got) || got[i].Resolve("") != want[i] {
+			t.Errorf("[%d]: got %q, want %q", i, got[i].Resolve(""), want[i])
 		}
 	}
 }
@@ -239,13 +243,13 @@ func TestCompileScenarioJSON_Inline(t *testing.T) {
 	input := &ScenarioJSON{
 		Chunk0: &ScenarioChunk0JSON{
 			Inline: []ScenarioInlineEntry{
-				{Index: 1, Text: "Sword"},
-				{Index: 2, Text: "Shield"},
+				{Index: 1, Text: NewLocalizedPlain("Sword")},
+				{Index: 2, Text: NewLocalizedPlain("Shield")},
 			},
 		},
 	}
 	jsonData, _ := json.Marshal(input)
-	compiled, err := CompileScenarioJSON(jsonData)
+	compiled, err := CompileScenarioJSON(jsonData, "")
 	if err != nil {
 		t.Fatalf("CompileScenarioJSON: %v", err)
 	}
@@ -257,11 +261,11 @@ func TestCompileScenarioJSON_Inline(t *testing.T) {
 	if result.Chunk0 == nil || len(result.Chunk0.Inline) != 2 {
 		t.Fatal("expected 2 inline entries")
 	}
-	if result.Chunk0.Inline[0].Text != "Sword" {
-		t.Errorf("got %q, want Sword", result.Chunk0.Inline[0].Text)
+	if got := result.Chunk0.Inline[0].Text.Resolve(""); got != "Sword" {
+		t.Errorf("got %q, want Sword", got)
 	}
-	if result.Chunk0.Inline[1].Text != "Shield" {
-		t.Errorf("got %q, want Shield", result.Chunk0.Inline[1].Text)
+	if got := result.Chunk0.Inline[1].Text.Resolve(""); got != "Shield" {
+		t.Errorf("got %q, want Shield", got)
 	}
 }
 
@@ -283,7 +287,7 @@ func TestScenarioRoundTrip_Subheader(t *testing.T) {
 		t.Fatalf("marshal: %v", err)
 	}
 
-	compiled, err := CompileScenarioJSON(jsonData)
+	compiled, err := CompileScenarioJSON(jsonData, "")
 	if err != nil {
 		t.Fatalf("compile: %v", err)
 	}
@@ -309,7 +313,7 @@ func TestScenarioRoundTrip_Inline(t *testing.T) {
 
 	s, _ := ParseScenarioBinary(original)
 	jsonData, _ := json.Marshal(s)
-	compiled, err := CompileScenarioJSON(jsonData)
+	compiled, err := CompileScenarioJSON(jsonData, "")
 	if err != nil {
 		t.Fatalf("compile: %v", err)
 	}
@@ -354,7 +358,7 @@ func TestScenarioRoundTrip_MetadataPreserved(t *testing.T) {
 
 	// Compile and parse again — metadata must survive
 	jsonData, _ := json.Marshal(s)
-	compiled, err := CompileScenarioJSON(jsonData)
+	compiled, err := CompileScenarioJSON(jsonData, "")
 	if err != nil {
 		t.Fatalf("compile: %v", err)
 	}
@@ -427,7 +431,7 @@ func TestScenarioRoundTrip_RealFiles(t *testing.T) {
 			}
 
 			// Compile JSON → binary
-			compiled, err := CompileScenarioJSON(jsonData)
+			compiled, err := CompileScenarioJSON(jsonData, "")
 			if err != nil {
 				t.Fatalf("CompileScenarioJSON: %v", err)
 			}
@@ -470,3 +474,75 @@ func TestScenarioRoundTrip_RealFiles(t *testing.T) {
 		})
 	}
 }
+
+// ── Phase C: localized scenario strings (#188) ───────────────────────────────
+
+// TestCompileScenarioJSON_LocalizedStrings exercises the LocalizedString
+// schema inside scenario subheader and inline chunks — the same plain-or-map
+// extension shipped for quests in phase B.
+func TestCompileScenarioJSON_LocalizedStrings(t *testing.T) {
+	input := &ScenarioJSON{
+		Chunk0: &ScenarioChunk0JSON{
+			Subheader: &ScenarioSubheaderJSON{
+				Type:     0x01,
+				Metadata: "AAAABBBB",
+				Strings: []LocalizedString{
+					mustLocalized(t, `{"jp":"クエスト","en":"Quest","fr":"Quete"}`),
+					mustLocalized(t, `"Plain String"`),
+				},
+			},
+		},
+	}
+	jsonData, err := json.Marshal(input)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+
+	// English request picks the en variant; the plain string stays plain.
+	compiledEN, err := CompileScenarioJSON(jsonData, "en")
+	if err != nil {
+		t.Fatalf("compile en: %v", err)
+	}
+	gotEN := extractStringsFromScenario(t, compiledEN)
+	wantEN := []string{"Quest", "Plain String"}
+	if len(gotEN) != len(wantEN) {
+		t.Fatalf("en string count: got %d, want %d", len(gotEN), len(wantEN))
+	}
+	for i := range wantEN {
+		if gotEN[i] != wantEN[i] {
+			t.Errorf("en [%d]: got %q, want %q", i, gotEN[i], wantEN[i])
+		}
+	}
+
+	// Japanese request picks the jp variant; plain still plain.
+	compiledJP, err := CompileScenarioJSON(jsonData, "jp")
+	if err != nil {
+		t.Fatalf("compile jp: %v", err)
+	}
+	gotJP := extractStringsFromScenario(t, compiledJP)
+	wantJP := []string{"クエスト", "Plain String"}
+	for i := range wantJP {
+		if gotJP[i] != wantJP[i] {
+			t.Errorf("jp [%d]: got %q, want %q", i, gotJP[i], wantJP[i])
+		}
+	}
+
+	// Spanish not provided → falls back to jp (the canonical fallback).
+	compiledES, err := CompileScenarioJSON(jsonData, "es")
+	if err != nil {
+		t.Fatalf("compile es: %v", err)
+	}
+	gotES := extractStringsFromScenario(t, compiledES)
+	if gotES[0] != "クエスト" {
+		t.Errorf("es fallback = %q, want jp fallback %q", gotES[0], "クエスト")
+	}
+}
+
+func mustLocalized(t *testing.T, src string) LocalizedString {
+	t.Helper()
+	var ls LocalizedString
+	if err := json.Unmarshal([]byte(src), &ls); err != nil {
+		t.Fatalf("unmarshal %q: %v", src, err)
+	}
+	return ls
+}
diff --git a/server/channelserver/sys_language_test.go b/server/channelserver/sys_language_test.go
index 63c4b3dbd..17d8f617f 100644
--- a/server/channelserver/sys_language_test.go
+++ b/server/channelserver/sys_language_test.go
@@ -193,3 +193,55 @@ func TestLangCompleteness(t *testing.T) {
 		})
 	}
 }
+
+// TestSessionI18n_Cached verifies that Session.I18n() returns an i18n table
+// resolved against the session's language and caches the pointer until
+// SetLang invalidates it (phase C of #188).
+func TestSessionI18n_Cached(t *testing.T) {
+	server := &Server{erupeConfig: &cfg.Config{Language: "en"}}
+	s := &Session{server: server}
+
+	en1 := s.I18n()
+	en2 := s.I18n()
+	if en1 != en2 {
+		t.Error("Session.I18n() should return the same pointer until SetLang")
+	}
+	if en1.language != "English" {
+		t.Errorf("server-default I18n = %q, want English", en1.language)
+	}
+
+	s.SetLang("jp")
+	jp := s.I18n()
+	if jp == en1 {
+		t.Error("SetLang should invalidate the cached I18n pointer")
+	}
+	if jp.language != "日本語" {
+		t.Errorf("after SetLang(jp) I18n = %q, want 日本語", jp.language)
+	}
+
+	// And another call returns the same (now-cached) jp pointer.
+	if s.I18n() != jp {
+		t.Error("Session.I18n() should be cached after SetLang rebuild")
+	}
+}
+
+// TestParseChatCommand_RepliesInSessionLanguage confirms the mechanical
+// s.server.i18n → s.I18n() refactor routes chat responses through the
+// session's language.
+func TestParseChatCommand_RepliesInSessionLanguage_Placeholder(t *testing.T) {
+	// Sanity: for a French session, the i18n table returned by I18n() must
+	// be the French one, and its commands.timer.enabled must not equal the
+	// English string.
+	server := &Server{erupeConfig: &cfg.Config{Language: "en"}}
+	s := &Session{server: server}
+	s.SetLang("fr")
+
+	frTable := s.I18n()
+	enTable := getLangStringsFor("en")
+	if frTable.commands.timer.enabled == enTable.commands.timer.enabled {
+		t.Error("fr and en timer.enabled strings should differ — refactor may have reverted")
+	}
+	if frTable.language != "Français" {
+		t.Errorf("session I18n language = %q, want Français", frTable.language)
+	}
+}
diff --git a/server/channelserver/sys_session.go b/server/channelserver/sys_session.go
index f31a61045..d432ea91e 100644
--- a/server/channelserver/sys_session.go
+++ b/server/channelserver/sys_session.go
@@ -49,6 +49,8 @@ type Session struct {
 	charID           uint32
 	userID           uint32
 	clientLang       string // Per-session language preference; empty = use server default
+	cachedI18n       *i18n  // Lazily populated by I18n(); invalidated on SetLang
+	cachedI18nLang   string // Lang the cachedI18n was built for
 	logKey           []byte
 	sessionStart     int64
 	courses          []mhfcourse.Course
@@ -126,12 +128,45 @@ func (s *Session) Lang() string {
 
 // SetLang updates the session's in-memory language preference. Persistence
 // to the database is the caller's responsibility (via userRepo.SetLanguage).
+// The cached i18n table is invalidated so the next I18n() call rebuilds
+// against the new language.
 func (s *Session) SetLang(lang string) {
 	s.Lock()
 	s.clientLang = lang
+	s.cachedI18n = nil
+	s.cachedI18nLang = ""
 	s.Unlock()
 }
 
+// I18n returns the i18n string table resolved against this session's
+// effective language (see Lang). The first call materializes the table via
+// getLangStringsFor and the result is cached on the session so hot-path
+// handlers (chat, mail, timer tick broadcasts) do not pay the allocation on
+// every packet. SetLang invalidates the cache.
+func (s *Session) I18n() *i18n {
+	s.Lock()
+	if s.cachedI18n != nil && s.cachedI18nLang == s.clientLang {
+		i := s.cachedI18n
+		s.Unlock()
+		return i
+	}
+	lang := s.clientLang
+	s.Unlock()
+	// Resolve lang (falls back to server default when empty).
+	effectiveLang := lang
+	if effectiveLang == "" {
+		effectiveLang = s.server.erupeConfig.Language
+	}
+	resolved := getLangStringsFor(effectiveLang)
+	s.Lock()
+	// Someone may have raced us — overwrite defensively, pointer value is
+	// still the one we just built so callers get a consistent view.
+	s.cachedI18n = &resolved
+	s.cachedI18nLang = lang
+	s.Unlock()
+	return &resolved
+}
+
 // Start starts the session packet send and recv loop(s).
 func (s *Session) Start() {
 	s.logger.Debug("New connection", zap.String("RemoteAddr", s.rawConn.RemoteAddr().String()))