diff --git a/program/Language.cs b/program/Language.cs
index 70695ae..a9afd86 100644
--- a/program/Language.cs
+++ b/program/Language.cs
@@ -1,12 +1,11 @@
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.IO;
 using Gtk;
 
 public class Language
 {
-    public static bool LanguageSwitchValue = false;
-
     private const string EngCssPath = "lang_eng.css";
     private const string JpnCssPath = "lang_jpn.css";
     private const string EngCsvPath = "info_eng.csv";
@@ -14,84 +13,134 @@
 
     private readonly Dictionary<string, string> _engText;
     private readonly Dictionary<string, string> _jpnText;
-    private readonly Dictionary<string, Button> _buttonsById;
-    public readonly CssProvider _languageCssProvider = new CssProvider();
-    private readonly Label _languageLabel;
+    private Dictionary<string, string> _text;
 
-     public Language(Dictionary<string, Button> buttonsById, Label languageLabel)
+    // widgets whose label is a plain CSV lookup
+    private readonly Dictionary<string, Widget> _widgets = new Dictionary<string, Widget>();
+
+    public readonly CssProvider _languageCssProvider = new CssProvider();
+
+    public bool IsEnglish { get; private set; }
+
+    /// <summary>Raised after every language change, so callers can rebuild state-dependent text.</summary>
+    public event EventHandler Changed;
+
+    public Language(bool isEnglish)
     {
-        _buttonsById = buttonsById;
-        _languageLabel = languageLabel;
         StyleContext.AddProviderForScreen(Gdk.Screen.Default, _languageCssProvider, 600);
 
+        _engText = LoadText(EngCsvPath);
+        _jpnText = LoadText(JpnCsvPath);
 
-        _engText = LoadButtonText(EngCsvPath);
-        _jpnText = LoadButtonText(JpnCsvPath);
+        // set before any widget is built, so ctor-time lookups are already correct
+        IsEnglish = isEnglish;
+        _text = isEnglish ? _engText : _jpnText;
     }
 
-    private Dictionary<string, string> LoadButtonText(string path)
+    // ---------- registration ----------
+
+    /// <summary>Label comes straight from the CSV key. Applied automatically on every change.</summary>
+    public void Register(string key, Widget widget)
+    {
+        if (widget == null) return;
+        widget.Name = key;              // enables #Key selectors in the lang CSS
+        _widgets[key] = widget;
+    }
+
+    /// <summary>Widget whose text the owner sets itself (state-dependent). Name only, no auto-apply.</summary>
+    public void RegisterDynamic(string key, Widget widget)
+    {
+        if (widget != null) widget.Name = key;
+    }
+
+    // ---------- lookup ----------
+
+    public string this[string key] { get { return Get(key); } }
+
+    public string Get(string key)
+    {
+        string value;
+        if (_text.TryGetValue(key, out value)) return value;
+
+        Console.WriteLine("Warning: missing text key '" + key + "'");
+        return key;
+    }
+
+    public string Format(string key, params object[] args)
+    {
+        string template = Get(key);
+        try
+        {
+            return string.Format(CultureInfo.InvariantCulture, template, args);
+        }
+        catch (FormatException)
+        {
+            Console.WriteLine("Warning: bad placeholder in text key '" + key + "'");
+            return template;
+        }
+    }
+
+    // ---------- apply ----------
+
+    public void Apply(bool isEnglish)
+    {
+        IsEnglish = isEnglish;
+        _text = isEnglish ? _engText : _jpnText;
+
+        foreach (var kvp in _widgets)
+        {
+            string value;
+            if (_text.TryGetValue(kvp.Key, out value))
+                SetText(kvp.Value, value);
+            else
+                Console.WriteLine("Warning: missing text key '" + kvp.Key + "'");
+        }
+
+        string cssPath = isEnglish ? EngCssPath : JpnCssPath;
+        if (File.Exists(cssPath))
+            _languageCssProvider.LoadFromPath(cssPath);
+        else
+            Console.WriteLine("Warning: CSS file not found: " + cssPath);
+
+        EventHandler handler = Changed;
+        if (handler != null) handler(this, EventArgs.Empty);
+    }
+
+    private static void SetText(Widget widget, string value)
+    {
+        Button button = widget as Button;           // also covers ToggleButton
+        if (button != null) { button.Label = value; return; }
+
+        Label label = widget as Label;
+        if (label != null) { label.Text = value; return; }
+
+        Console.WriteLine("Warning: don't know how to set text on " + widget.GetType().Name);
+    }
+
+    // ---------- csv ----------
+
+    private Dictionary<string, string> LoadText(string path)
     {
         var result = new Dictionary<string, string>();
+
         if (!File.Exists(path))
         {
-            Console.WriteLine($"Warning: text file not found: {path}");
+            Console.WriteLine("Warning: text file not found: " + path);
             return result;
         }
 
-        var lines = File.ReadAllLines(path);
-        for (int i = 1; i < lines.Length; i++)
+        string[] lines = File.ReadAllLines(path);
+        for (int i = 1; i < lines.Length; i++)      // row 0 is the header
         {
-            var line = lines[i].Trim();
-            if (string.IsNullOrEmpty(line)) continue;
-            var parts = line.Split(new[] { ',' }, 2);
+            string line = lines[i].Trim();
+            if (string.IsNullOrEmpty(line) || line.StartsWith("#")) continue;
+
+            string[] parts = line.Split(new[] { ',' }, 2);
             if (parts.Length < 2) continue;
-            result[parts[0]] = parts[1];
+
+            result[parts[0].Trim()] = parts[1];     // value keeps any commas
         }
+
         return result;
     }
-
-    public void ApplyLanguage(bool isEnglish)
-    {
-        var text = isEnglish ? _engText : _jpnText;
-        string cssPath = isEnglish ? EngCssPath : JpnCssPath;
-
-        foreach (var kvp in _buttonsById)
-            if (text.TryGetValue(kvp.Key, out var buttonText))
-                kvp.Value.Label = buttonText;
-
-        if (File.Exists(cssPath))
-            _languageCssProvider.LoadFromPath(cssPath);
-        else
-            Console.WriteLine($"Warning: CSS file not found: {cssPath}");
-
-        _languageLabel.Text = isEnglish ? "あ" : "A";
-    }
-
-    //for others
-     public Language(Dictionary<string, Button> buttonsById)
-    {
-        _buttonsById = buttonsById;
-        StyleContext.AddProviderForScreen(Gdk.Screen.Default, _languageCssProvider, 600);
-
-
-        _engText = LoadButtonText(EngCsvPath);
-        _jpnText = LoadButtonText(JpnCsvPath);
-    }
-
-    
-    public void ApplyLanguages(bool isEnglish)
-    {
-        var text = isEnglish ? _engText : _jpnText;
-        string cssPath = isEnglish ? EngCssPath : JpnCssPath;
-
-        foreach (var kvp in _buttonsById)
-            if (text.TryGetValue(kvp.Key, out var buttonText))
-                kvp.Value.Label = buttonText;
-
-        if (File.Exists(cssPath))
-            _languageCssProvider.LoadFromPath(cssPath);
-        else
-            Console.WriteLine($"Warning: CSS file not found: {cssPath}");
-
-    }
 }
\ No newline at end of file
diff --git a/program/MainWindow.cs b/program/MainWindow.cs
index e87516b..b68f449 100644
--- a/program/MainWindow.cs
+++ b/program/MainWindow.cs
@@ -38,7 +38,8 @@
 
     // private Dictionary<string, string> _engText;
     // private Dictionary<string, string> _jpnText;
-    private Dictionary<string, Button> _buttonsById;
+    // private Dictionary<string, Button> _buttonsById;
+    private bool _connected;
 
     private readonly ArduinoConnection _arduino = new ArduinoConnection();
     internal SettingsWindow _settingsWindow;
@@ -84,31 +85,46 @@
 
         _arduino.ConnectionChanged += OnArduinoConnectionChanged;
 
-        _buttonsById = new Dictionary<string, Button>
-        {
-            { "Option1Button", Option1Button },
-            { "Option2Button", Option2Button },
-            { "Option3Button", Option3Button },
-            { "CloseButton",   CloseButton   },
-            { "SettingButton", SettingButton },
-        };
 
-        // CSS ID selectors (#Option1Button etc.) need the widget Name set explicitly
-        foreach (var kvp in _buttonsById)
-            kvp.Value.Name = kvp.Key;
 
-        // _engText = LoadButtonText("info_eng.csv");
-        // _jpnText = LoadButtonText("info_jpn.csv");
+        // // _buttonsById = new Dictionary<string, Button>
+        // // {
+        // //     { "Option1Button", Option1Button },
+        // //     { "Option2Button", Option2Button },
+        // //     { "Option3Button", Option3Button },
+        // //     { "CloseButton",   CloseButton   },
+        // //     { "SettingButton", SettingButton },
+        // // };
 
-        _Language = new Language(_buttonsById,LanguageLabel);
+        // // CSS ID selectors (#Option1Button etc.) need the widget Name set explicitly
+        // foreach (var kvp in _buttonsById)
+        //     kvp.Value.Name = kvp.Key;
 
-        // _Language.ApplyLanguage(LanguageSwitch.Active);
-        
-        _settingsWindow = new SettingsWindow(builder, _arduino);
+        // // _engText = LoadButtonText("info_eng.csv");
+        // // _jpnText = LoadButtonText("info_jpn.csv");
+
+        // _Language = new Language(_buttonsById,LanguageLabel);
+
+        // // _Language.ApplyLanguage(LanguageSwitch.Active);
+
+        _Language = new Language(LanguageToggle.Active);
+        _Language.Register("Option1Button",  Option1Button);
+        _Language.Register("Option2Button",  Option2Button);
+        _Language.Register("Option3Button",  Option3Button);
+        _Language.Register("CloseButton",    CloseButton);
+        _Language.Register("SettingButton",  SettingButton);
+        _Language.Register("LanguageLabel",  LanguageLabel);
+        _Language.Register("LanguageToggle", LanguageToggle);
+        _Language.RegisterDynamic("ConnectionIcon", ConnectionIcon);
+
+        _settingsWindow = new SettingsWindow(builder, _arduino, _Language);
         _settingsWindow.BackRequested += OnSettingsClosed;
 
-        // single source of truth: the toggle drives both pages
-        ApplyLanguageEverywhere(LanguageToggle.Active);
+        _Language.Changed += (s, e) => OnArduinoConnectionChanged(_connected);
+        _Language.Apply(LanguageToggle.Active);
+
+        // // single source of truth: the toggle drives both pages
+        // ApplyLanguageEverywhere(LanguageToggle.Active);
 
         RootNoteBook.ShowTabs    = false;
         RootNoteBook.ShowBorder  = false;
@@ -147,6 +163,7 @@
 
     private void OnArduinoConnectionChanged(bool connected)
     {
+        _connected = connected;
         if (ConnectionIcon == null) return;
 
         ConnectionIcon.SetFromIconName(
@@ -154,36 +171,36 @@
             IconSize.Dnd);
 
         ConnectionIcon.TooltipText = connected
-            ? $"Connected to {_arduino.PortName}"
-            : "Device not connected";
+            ? _Language.Format("ConnectionIcon.Connected", _arduino.PortName)
+            : _Language["ConnectionIcon.Disconnected"];
     }
 
     // ---------- localisation ----------
 
-    private Dictionary<string, string> LoadButtonText(string path)
-    {
-        var result = new Dictionary<string, string>();
+    // private Dictionary<string, string> LoadButtonText(string path)
+    // {
+    //     var result = new Dictionary<string, string>();
 
-        if (!File.Exists(path))
-        {
-            Console.WriteLine($"Warning: text file not found: {path}");
-            return result;
-        }
+    //     if (!File.Exists(path))
+    //     {
+    //         Console.WriteLine($"Warning: text file not found: {path}");
+    //         return result;
+    //     }
 
-        var lines = File.ReadAllLines(path);
-        for (int i = 1; i < lines.Length; i++) // skip header row
-        {
-            var line = lines[i].Trim();
-            if (string.IsNullOrEmpty(line)) continue;
+    //     var lines = File.ReadAllLines(path);
+    //     for (int i = 1; i < lines.Length; i++) // skip header row
+    //     {
+    //         var line = lines[i].Trim();
+    //         if (string.IsNullOrEmpty(line)) continue;
 
-            var parts = line.Split(new[] { ',' }, 2);
-            if (parts.Length < 2) continue;
+    //         var parts = line.Split(new[] { ',' }, 2);
+    //         if (parts.Length < 2) continue;
 
-            result[parts[0]] = parts[1];
-        }
+    //         result[parts[0]] = parts[1];
+    //     }
 
-        return result;
-    }
+    //     return result;
+    // }
 
     // private void ApplyLanguage(bool isEnglish)
     // {
@@ -282,15 +299,15 @@
         Console.WriteLine("Exam Mode selected");
     }
 
-     private void OnLanguageToggled(object sender, EventArgs e)
+      private void OnLanguageToggled(object sender, EventArgs e)
     {
-        ApplyLanguageEverywhere(LanguageToggle.Active);
+        _Language.Apply(LanguageToggle.Active);
     }
 
-    private void ApplyLanguageEverywhere(bool isEnglish)
-    {
-        Language.LanguageSwitchValue = isEnglish;
-        _Language.ApplyLanguage(isEnglish);
-        _settingsWindow?._Language?.ApplyLanguages(isEnglish);
-    }
+    // private void ApplyLanguageEverywhere(bool isEnglish)
+    // {
+    //     Language.LanguageSwitchValue = isEnglish;
+    //     _Language.ApplyLanguage(isEnglish);
+    //     _settingsWindow?._Language?.ApplyLanguages(isEnglish);
+    // }
 }
\ No newline at end of file
diff --git a/program/SettingWindow.cs b/program/SettingWindow.cs
index 1fed549..f39a427 100644
--- a/program/SettingWindow.cs
+++ b/program/SettingWindow.cs
@@ -15,9 +15,11 @@
     [UI] private Label      LogLabel         = null;
     [UI] private TextView   LogtextBox       = null;
 
-    private readonly Dictionary<string, Button> _buttonsById;
-    private readonly Dictionary<string, Label> _labelsById;
-    internal Language _Language;
+    // private readonly Dictionary<string, Button> _buttonsById;
+    // private readonly Dictionary<string, Label> _labelsById;
+    // internal Language _Language;
+    private readonly Language _lang;
+    private bool _connected;
 
     private const int MaxLogLines = 500;
 
@@ -28,14 +30,15 @@
     public event EventHandler BackRequested;
 
 
-    public SettingsWindow(Builder builder, ArduinoConnection arduino)
+     public SettingsWindow(Builder builder, ArduinoConnection arduino, Language language)
     {
         builder.Autoconnect(this);
         _arduino = arduino;
+        _lang = language;
 
         // Title = "Settings";
-        ComPortLabel.Text = "COM Port";
-        LogLabel.Text = "Log";
+        // ComPortLabel.Text = "COM Port";
+        // LogLabel.Text = "Log";
         LogtextBox.Editable = false;
         LogtextBox.WrapMode = WrapMode.WordChar;
 
@@ -50,20 +53,29 @@
         _arduino.LineReceived      += OnLineReceived;
         _arduino.ConnectionChanged += OnConnectionChanged;
 
-         _buttonsById = new Dictionary<string, Button>
-         {
-            { "ConnectButton", ConnectButton },
-            { "AutoConnectButton", AutoConnectButton },
-            { "RefreshButton", RefreshButton },
-            { "BackButton",   BackButton   },
-         };
+        _lang.Register("ComPortLabel",      ComPortLabel);
+        _lang.Register("LogLabel",          LogLabel);
+        _lang.Register("AutoConnectButton", AutoConnectButton);
+        _lang.Register("RefreshButton",     RefreshButton);
+        _lang.Register("BackButton",        BackButton);
+        _lang.RegisterDynamic("ConnectButton", ConnectButton);   // set in OnConnectionChanged
+        _lang.RegisterDynamic("StatusLabel",   StatusLabel);
+        _lang.Changed += (s, e) => OnConnectionChanged(_connected);
 
-        // CSS ID selectors (#Option1Button etc.) need the widget Name set explicitly
-        foreach (var kvp in _buttonsById)
-            kvp.Value.Name = kvp.Key;
+        //  _buttonsById = new Dictionary<string, Button>
+        //  {
+        //     { "ConnectButton", ConnectButton },
+        //     { "AutoConnectButton", AutoConnectButton },
+        //     { "RefreshButton", RefreshButton },
+        //     { "BackButton",   BackButton   },
+        //  };
+
+        // // CSS ID selectors (#Option1Button etc.) need the widget Name set explicitly
+        // foreach (var kvp in _buttonsById)
+        //     kvp.Value.Name = kvp.Key;
         
-        _Language = new Language(_buttonsById);
-        // _Language.ApplyLanguages(Language.LanguageSwitchValue); 
+        // _Language = new Language(_buttonsById);
+        // // _Language.ApplyLanguages(Language.LanguageSwitchValue); 
 
         RefreshPorts();
         OnConnectionChanged(_arduino.IsOpen);
@@ -82,11 +94,11 @@
         if (_ports.Length > 0)
         {
             ComPortComboBox.Active = 0;
-            AppendLog($"{_ports.Length} port(s) found");
+            AppendLog(_lang.Format("Log.PortsFound", _ports.Length));
         }
         else
         {
-            AppendLog("No serial ports found");
+            AppendLog(_lang["Log.NoPorts"]);
         }
     }
 
@@ -101,7 +113,7 @@
         string port = ComPortComboBox.ActiveText;
         if (string.IsNullOrEmpty(port))
         {
-            AppendLog("Select a COM port first");
+            AppendLog(_lang["Log.SelectPort"]);
             return;
         }
         _arduino.Connect(port);
@@ -111,7 +123,7 @@
     {
         AutoConnectButton.Sensitive = false;
         ConnectButton.Sensitive = false;
-        AppendLog("Scanning ports for device...");
+        AppendLog(_lang["Log.Scanning"]);
 
         string found = await _arduino.DetectPortAsync();
 
@@ -123,7 +135,7 @@
         }
         else
         {
-            AppendLog("Device not found — use manual connection");
+            AppendLog(_lang["Log.DeviceNotFound"]);
         }
 
         AutoConnectButton.Sensitive = true;
@@ -152,10 +164,15 @@
 
     private void OnConnectionChanged(bool connected)
     {
-        ConnectButton.Label = connected ? "Disconnect" : "Connect";
+        _connected = connected;
+
+        ConnectButton.Label = connected
+            ? _lang["ConnectButton.Disconnect"]
+            : _lang["ConnectButton.Connect"];
+
         StatusLabel.Text = connected
-            ? $"Connected ({_arduino.PortName})"
-            : "Disconnected";
+            ? _lang.Format("StatusLabel.Connected", _arduino.PortName)
+            : _lang["StatusLabel.Disconnected"];
 
         ComPortComboBox.Sensitive = !connected;
         RefreshButton.Sensitive   = !connected;
@@ -171,8 +188,8 @@
         if (line.StartsWith("Send Status:")) return;
         if (line.StartsWith("\u2713") || line.StartsWith("\u2717")) return;
 
-        if (line.Contains("ESPNOW_CONNECTED"))    { AppendLog("[ESP-NOW] Peer connected");    return; }
-        if (line.Contains("ESPNOW_DISCONNECTED")) { AppendLog("[ESP-NOW] Peer disconnected"); return; }
+        if (line.Contains("ESPNOW_CONNECTED"))    { AppendLog(_lang["Log.EspNowConnected"]);    return; }
+        if (line.Contains("ESPNOW_DISCONNECTED")) { AppendLog(_lang["Log.EspNowDisconnected"]); return; }
 
         AppendLog(line);
     }
diff --git a/program/info_eng.csv b/program/info_eng.csv
index 3a0481a..a7bb3e8 100644
--- a/program/info_eng.csv
+++ b/program/info_eng.csv
@@ -1,11 +1,26 @@
-ButtonId,Text
+key,text
 Option1Button,Normal Session
 Option2Button,Position Recording Mode
 Option3Button,Exam Mode
-CloseButton,Close
 SettingButton,Settings
-ConnectButton,Connect
-AutoConnectButton,Auto Connect
-RefreshButton, Refresh Port
+CloseButton,Close
+LanguageLabel,Language
+LanguageToggle,あ
+ComPortLabel,COM Port
 LogLabel,Log
+AutoConnectButton,Auto Connect
+RefreshButton,Refresh Ports
 BackButton,Back
+ConnectButton.Connect,Connect
+ConnectButton.Disconnect,Disconnect
+StatusLabel.Connected,Connected ({0})
+StatusLabel.Disconnected,Disconnected
+ConnectionIcon.Connected,Connected to {0}
+ConnectionIcon.Disconnected,Device not connected
+Log.PortsFound,{0} port(s) found
+Log.NoPorts,No serial ports found
+Log.SelectPort,Select a COM port first
+Log.Scanning,Scanning ports for device...
+Log.DeviceNotFound,Device not found — use manual connection
+Log.EspNowConnected,[ESP-NOW] Peer connected
+Log.EspNowDisconnected,[ESP-NOW] Peer disconnected
\ No newline at end of file
diff --git a/program/info_jpn.csv b/program/info_jpn.csv
index 1d4e6e8..5cac763 100644
--- a/program/info_jpn.csv
+++ b/program/info_jpn.csv
@@ -1,11 +1,26 @@
-ButtonId,Text
+key,text
 Option1Button,通常セッション
 Option2Button,位置記録モード
 Option3Button,試験モード
-CloseButton,閉じる
 SettingButton,設定
-ConnectButton,接続
+CloseButton,終了
+LanguageLabel,言語
+LanguageToggle,A
+ComPortLabel,COMポート
+LogLabel,ログ
 AutoConnectButton,自動接続
-RefreshButton, ポートの更新
-LogLabel,情報 
+RefreshButton,ポート更新
 BackButton,戻る
+ConnectButton.Connect,接続
+ConnectButton.Disconnect,切断
+StatusLabel.Connected,接続済み ({0})
+StatusLabel.Disconnected,未接続
+ConnectionIcon.Connected,{0} に接続しました
+ConnectionIcon.Disconnected,デバイスが接続されていません
+Log.PortsFound,ポートが {0} 個見つかりました
+Log.NoPorts,シリアルポートが見つかりません
+Log.SelectPort,COMポートを選択してください
+Log.Scanning,デバイスを検索中...
+Log.DeviceNotFound,デバイスが見つかりません — 手動で接続してください
+Log.EspNowConnected,[ESP-NOW] 相手が接続しました
+Log.EspNowDisconnected,[ESP-NOW] 相手が切断しました
\ No newline at end of file