var bld = WebApplication.CreateBuilder(args);
bld.Services
   .SwaggerDocument()
   .AddFastEndpoints()
   .AddLocalization();

var app = bld.Build();
app.UseFastEndpoints()
   .UseSwaggerGen()
   .UseRequestLocalization();
app.Run();

public partial class Program;

sealed class MyRequest
{
    public int Id { get; set; }

    public sealed class MyValidator : Validator<MyRequest>
    {
        public MyValidator(IStringLocalizer<MyValidator> localizer)
        {
            RuleFor(r => r.Id).GreaterThan(0).WithMessage(r => localizer["InvalidId"].Value);
        }
    }
}

sealed class MyEndpoint : Endpoint<MyRequest>
{
    public override void Configure()
    {
        Post("test");
        AllowAnonymous();
    }

    public override async Task HandleAsync(MyRequest r, CancellationToken c)
    {
        await SendAsync(r);
    }
}