Startup.cs

public class Startup
{
    private static readonly string _defaultLanguage = "en";
    private static readonly List<CultureInfo> _supportedCultures = new List<CultureInfo> { new CultureInfo(_defaultLanguage) };

    public void ConfigureServices(IServiceCollection services)
    {
        ...
        services.AddControllers();

        // Dictionary registrations
        services.Configure<SitecoreLocalizerOptions>(options => options.Cultures = _supportedCultures);
        services.AddHttpClient<ISitecoreLocalizer, SitecoreLocalizer>("sitecoreLocalizer", client =>
        {
            client.BaseAddress = Configuration.DictionaryServiceUri;
        });

        services.AddTransient<ISitecoreLocalizer, SitecoreLocalizer>();
        services.AddTransient<IStringLocalizer, SitecoreLocalizer>();
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.UseEndpoints(endpoints =>
        {
            ...
            // Open the endpoint to Sitecore CM publishing web hook
            endpoints.MapControllerRoute(
                "localization",
                "api/localization/reload",
                new { controller = "Localization", action = "Reload" }
            );
            ...
        });

        // Initialize the dictionary cache
        Task.Run(async () => await app.ApplicationServices.GetRequiredService<ISitecoreLocalizer>().Reload()).Wait();
    }
}