Implement auto-switching to English when the option is enabled

Flow.Launcher.Infrastructure/NativeMethods.txt

@@ -46,4 +46,13 @@ GetMonitorInfo
 MONITORINFOEXW
 
 WM_ENTERSIZEMOVE
-WM_EXITSIZEMOVE
+WM_EXITSIZEMOVE
+
+GetKeyboardLayout
+GetWindowThreadProcessId
+ActivateKeyboardLayout
+GetKeyboardLayoutList
+
+PostMessage
+WM_INPUTLANGCHANGEREQUEST
+INPUTLANGCHANGE_FORWARD

Flow.Launcher.Infrastructure/Win32Helper.cs

@@ -1,14 +1,17 @@
 using System;
 using System.ComponentModel;
+using System.Linq;
 using System.Runtime.InteropServices;
 using System.Windows;
 using System.Windows.Interop;
 using System.Windows.Media;
 using Windows.Win32;
 using Windows.Win32.Foundation;
 using Windows.Win32.Graphics.Dwm;
+using Windows.Win32.UI.Input.KeyboardAndMouse;
 using Windows.Win32.UI.WindowsAndMessaging;
 using Flow.Launcher.Infrastructure.UserSettings;
+using Point = System.Windows.Point;
 
 namespace Flow.Launcher.Infrastructure
 {
@@ -63,7 +66,7 @@ public static unsafe bool DWMSetDarkModeForWindow(Window window, bool useDarkMod
         }
 
         /// <summary>
-        /// 
+        ///
         /// </summary>
         /// <param name="window"></param>
         /// <param name="cornerType">DoNotRound, Round, RoundSmall, Default</param>
@@ -317,5 +320,116 @@ internal static HWND GetWindowHandle(Window window, bool ensure = false)
         }
 
         #endregion
+
+        #region Keyboard Layout
+
+        // https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-lcid/70feba9f-294e-491e-b6eb-56532684c37f
+        private static readonly uint[] EnglishLanguageIds =
+        {
+            0x0009, 0x0409, 0x0809, 0x0C09, 0x1009, 0x1409, 0x1809, 0x1C09, 0x2009, 0x2409, 0x2809, 0x2C09, 0x3009,
+            0x3409, 0x3C09, 0x4009, 0x4409, 0x4809, 0x4C09,
+        };
+
+        private static readonly uint[] ImeLanguageIds =
+        {
+            0x0004, 0x7804, 0x0804, 0x1004, 0x7C04, 0x0C04, 0x1404, 0x0404, 0x0011, 0x0411, 0x0012, 0x0412,
+        };
+
+        private const uint KeyboardLayoutLoWord = 0xFFFF;
+
+        // Store the previous keyboard layout
+        private static HKL _previousLayout;
+
+        private static unsafe HKL FindEnglishKeyboardLayout()
+        {
+            // Get the number of keyboard layouts
+            int count = PInvoke.GetKeyboardLayoutList(0, null);
+            if (count <= 0) return HKL.Null;
+
+            // Get all keyboard layouts
+            var handles = new HKL[count];
+            fixed (HKL* h = handles)
+            {
+                var result = PInvoke.GetKeyboardLayoutList(count, h);
+                if (result == 0)
+                {
+                    throw new Win32Exception(Marshal.GetLastWin32Error());
+                }
+            }
+
+            // Look for any English keyboard layout
+            foreach (var hkl in handles)
+            {
+                // The lower word contains the language identifier
+                var langId = (uint)hkl.Value & KeyboardLayoutLoWord;
+
+                // Check if it's an English layout
+                if (EnglishLanguageIds.Contains(langId))
+                {
+                    return hkl;
+                }
+            }
+
+            return HKL.Null;
+        }
+
+        /// <summary>
+        /// Switches the keyboard layout to English if available.
+        /// </summary>
+        /// <param name="backupPrevious">If true, the current keyboard layout will be stored for later restoration.</param>
+        /// <exception cref="Win32Exception">Thrown when there's an error getting the window thread process ID.</exception>
+        public static unsafe void SwitchToEnglishKeyboardLayout(bool backupPrevious)
+        {
+            // Find an installed English layout
+            var enHKL = FindEnglishKeyboardLayout();
+
+            // No installed English layout found
+            if (enHKL == HKL.Null) return;
+
+            // Get the current window thread ID
+            var threadId = PInvoke.GetWindowThreadProcessId(PInvoke.GetForegroundWindow());
+            if (threadId == 0) throw new Win32Exception(Marshal.GetLastWin32Error());
+
+            // If the current layout has an IME mode, disable it without switching to another layout.
+            // This is needed because for languages with IME mode, Flow Launcher just temporarily disables
+            // the IME mode instead of switching to another layout.
+            var currentLayout = PInvoke.GetKeyboardLayout(threadId);
+            var currentLayoutCode = (uint)currentLayout.Value & KeyboardLayoutLoWord;
+            if (ImeLanguageIds.Contains(currentLayoutCode))
+            {
+                return;
+            }
+
+            // Backup current keyboard layout
+            if (backupPrevious)
+            {
+                _previousLayout = currentLayout;
+            }
+
+            // Switch to English layout
+            PInvoke.ActivateKeyboardLayout(enHKL, 0);
+        }
+
+        /// <summary>
+        /// Restores the previously backed-up keyboard layout.
+        /// If it wasn't backed up or has already been restored, this method does nothing.
+        /// </summary>
+        public static void RestorePreviousKeyboardLayout()
+        {
+            if (_previousLayout == HKL.Null) return;
+
+            var hwnd = PInvoke.GetForegroundWindow();
+            if (hwnd == HWND.Null) return;
+
+            PInvoke.PostMessage(
+                hwnd,
+                PInvoke.WM_INPUTLANGCHANGEREQUEST,
+                PInvoke.INPUTLANGCHANGE_FORWARD,
+                _previousLayout.Value
+            );
+            _previousLayout = HKL.Null;
+        }
+
+        #endregion
     }
 }

Flow.Launcher/ViewModel/MainViewModel.cs

@@ -1373,6 +1373,11 @@ public void Show()
                 MainWindowOpacity = 1;
                 MainWindowVisibilityStatus = true;
                 VisibilityChanged?.Invoke(this, new VisibilityChangedEventArgs { IsVisible = true });
+
+                if (StartWithEnglishMode)
+                {
+                    Win32Helper.SwitchToEnglishKeyboardLayout(true);
+                }
             });
         }
 
@@ -1441,7 +1446,12 @@ public async void Hide()
                 // 📌 Apply DWM Cloak (Completely hide the window)
                 Win32Helper.DWMSetCloakForWindow(mainWindow, true);
             }
-
+
+            if (StartWithEnglishMode)
+            {
+                Win32Helper.RestorePreviousKeyboardLayout();
+            }
+
             await Task.Delay(50);
 
             // Update WPF properties