getting error Kentico.PageBuilder.LocalizationScript could not be found in the route collection

Where are you seeing this error?

How do you initialize the PageBuilder in your code? In your app start something along the lines of

protected void Application_Start()
{
    ApplicationBuilder builder = ApplicationBuilder.Current;
    builder.UsePageBuilder();

https://docs.kentico.com/k12/developing-websites/page-builder-development

Did you define any routes before the default Kentico routes:

            // Map routes to Kentico HTTP handlers first as some Kentico URLs might be matched by the default ASP.NET MVC route resulting in displaying pages without images
            routes.Kentico().MapRoutes();