Program.cs

using StudyJournalPro.Properties.Localization;
using StudyJournalPro.StudyJournalPro.Business;
using StudyJournalPro.StudyJournalPro.DataAccess;
using StudyJournalPro.StudyJournalPro.Presentation;
using System.Globalization;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace StudyJournalPro
{
    internal static class Program
    {
        private static Mutex mutex = null;

        // Windows API importlarý
        [DllImport("user32.dll", SetLastError = true)]
        private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

        [DllImport("user32.dll")]
        private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

        [DllImport("user32.dll")]
        private static extern bool SetForegroundWindow(IntPtr hWnd);

        private const int SW_RESTORE = 9;


        /// <summary>
        ///  The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            // Ayarlarda saklanan dil kodunu oku (ör. "tr-TR" veya "en-US")

            // Kullanýcýnýn son seçtiði dili uygula
            string savedCulture = Properties.Settings.Default.AppLanguage;
            //MessageBox.Show("Uygulama baþlangýcýnda okunan dil: '" + savedCulture + "'");

            if (!string.IsNullOrEmpty(savedCulture))
            {
                try
                {
                    System.Threading.Thread.CurrentThread.CurrentUICulture = new CultureInfo(savedCulture); //new System.Globalization.CultureInfo(savedCulture);
                    System.Threading.Thread.CurrentThread.CurrentCulture = new CultureInfo(savedCulture);

                }

                catch
                {
                }


            }


            // To customize application configuration such as set high DPI settings or default font,
            // see https://aka.ms/applicationconfiguration.

            const string appName = "StudyJournalPro";
            mutex = new Mutex(true, appName, out bool createdNew);

            if (!createdNew)
            {
                // Çalýþan uygulamanýn ana penceresini bul
                IntPtr hWnd = FindWindow(null, Localization.lblAppName); // <-- Form'un Title Text'i ile eþleþmeli

                if (hWnd != IntPtr.Zero)
                {
                    // Eðer gizliyse geri getir
                    ShowWindow(hWnd, SW_RESTORE);

                    // Öne al
                    SetForegroundWindow(hWnd);
                }

                return;
            }

            ApplicationConfiguration.Initialize();

            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            // Business katmaný için repository oluþtur
            IChronometerRepository repository = new SQLiteChronometerRepository();

            // Business servisini oluþtur (Dependency Injection)
            IChronometerService kronometreService = new ChronometerManager(repository);

            // Formu sadece service üzerinden baþlat


            Application.Run(new SideBarForm(kronometreService));//  eski versiyon 





        }
    }
}