I'm trying to get data annotations validation messages in Portuguese (pt-BR) but they remain in English even after setting the culture.

Here's what I've tried - in Program.cs:

var builder = WebApplication.CreateBuilder(args);

// Setting default culture
var culturaPtBr = new CultureInfo("pt-BR");
CultureInfo.DefaultThreadCurrentCulture = culturaPtBr;
CultureInfo.DefaultThreadCurrentUICulture = culturaPtBr;

// Configuring RequestLocalization
builder.Services.Configure<RequestLocalizationOptions>(options =>
{
    options.DefaultRequestCulture = new RequestCulture("pt-BR");
    options.SupportedCultures = new List<CultureInfo> { new("pt-BR") };
    options.SupportedUICultures = new List<CultureInfo> { new("pt-BR") };
    options.FallBackToParentCultures = false;
    options.FallBackToParentUICultures = false;
});

var app = builder.Build();

// Adding localization middleware
app.UseRequestLocalization();

My model class:

public class LoginRequest
{
    [Required]
    public string Usuario { get; set; }

    [Required]
    [StringLength(100, MinimumLength = 6)]
    public string Senha { get; set; }
}

When validation fails, I still get messages in English like "The Usuario field is required" instead of the Portuguese equivalent. I don't want to customize each validation message manually. How can I make data annotations use the built-in Portuguese translations?

Environment: ASP.NET Core 8 Core Web API

What am I missing?

I'm trying to get data annotations validation messages in Portuguese (pt-BR) but they remain in English even after setting the culture.

Here's what I've tried - in Program.cs:

var builder = WebApplication.CreateBuilder(args);

// Setting default culture
var culturaPtBr = new CultureInfo("pt-BR");
CultureInfo.DefaultThreadCurrentCulture = culturaPtBr;
CultureInfo.DefaultThreadCurrentUICulture = culturaPtBr;

// Configuring RequestLocalization
builder.Services.Configure<RequestLocalizationOptions>(options =>
{
    options.DefaultRequestCulture = new RequestCulture("pt-BR");
    options.SupportedCultures = new List<CultureInfo> { new("pt-BR") };
    options.SupportedUICultures = new List<CultureInfo> { new("pt-BR") };
    options.FallBackToParentCultures = false;
    options.FallBackToParentUICultures = false;
});

var app = builder.Build();

// Adding localization middleware
app.UseRequestLocalization();

My model class:

public class LoginRequest
{
    [Required]
    public string Usuario { get; set; }

    [Required]
    [StringLength(100, MinimumLength = 6)]
    public string Senha { get; set; }
}

When validation fails, I still get messages in English like "The Usuario field is required" instead of the Portuguese equivalent. I don't want to customize each validation message manually. How can I make data annotations use the built-in Portuguese translations?

Environment: ASP.NET Core 8 Core Web API

What am I missing?

• asp-core-webapi
• data-annotations
• asp-core-8
• asp-core-localization

1 Answer 1

When validation fails, I still get messages in English like "The Usuario field is required" instead of the Portuguese equivalent. I don't want to customize each validation message manually. How can I make data annotations use the built-in Portuguese translations?

The issue might relate that you didn't provide the Resource File for Localization Data Annotation Messages.

You can check this tutorial: DataAnnotations localization. When configure the localization, we can use the following code to set the resources path to "Resources".

builder.Services.AddLocalization(options => options.ResourcesPath = "Resources");

And use AddDataAnnotationsLocalization adds support for localized DataAnnotations validation messages through IStringLocalizer abstractions.

Based on the official localization sample, I add an API controller and test the localized DataAnnotation validation with the following steps:

1. Add a Product class in the Models folder:

    public class Product
    {
        [Required(ErrorMessage = "ProductNameRequired")]
        public string Name { get; set; }
   
        [Range(1, 1000, ErrorMessage = "PriceRangeError")]
        public decimal Price { get; set; }
    }
   

2. In the Resources\SharedResource.fr.resx resource file, add the translated value:

3. In the Program.cs file, use the following code to configure the localization:

    builder.Services.AddLocalization(options => options.ResourcesPath = "Resources");
   
    builder.Services.AddMvc()
        .AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix)
        .AddDataAnnotationsLocalization();
    // </snippet_LocalizationConfigurationServices>
   
    builder.Services.AddControllers()
        .AddDataAnnotationsLocalization(options =>
        {
            var factory = builder.Services.BuildServiceProvider()
                .GetRequiredService<IStringLocalizerFactory>();
            var localizer = factory.Create(typeof(SharedResource));
            options.DataAnnotationLocalizerProvider = (type, factory) => localizer;
        }); 
   
   
    builder.Services.AddTransient<IEmailSender, AuthMessageSender>();
    builder.Services.AddTransient<ISmsSender, AuthMessageSender>();
   
    // <snippet_RequestLocalizationOptionsConfiguration>
    builder.Services.Configure<RequestLocalizationOptions>(options =>
    {
        var supportedCultures = new[] { "fr", "en-US"};
        options.SetDefaultCulture(supportedCultures[0])
            .AddSupportedCultures(supportedCultures)
            .AddSupportedUICultures(supportedCultures);
    });
    // </snippet_RequestLocalizationOptionsConfiguration>
    builder.Services.AddEndpointsApiExplorer();
    builder.Services.AddSwaggerGen(c =>
    {
        c.SwaggerDoc("v1", new Microsoft.OpenApi.Models.OpenApiInfo { Title = "Global Header Example", Version = "v1" }); 
    });
    var app = builder.Build();
   
    var localizationOptions = app.Services.GetRequiredService<IOptions<RequestLocalizationOptions>>();
    app.UseRequestLocalization(localizationOptions.Value);
   

4. Add an API to check the validation:

    [Route("api/[controller]")]
    [ApiController]
    public class TodoController : ControllerBase
    {
        [HttpPost]
        public IActionResult AddProduct(Product product)
        {
   
            return Ok(product);
        }
    }
   

Then, when access the API, the output as below (the language/culture send via cookie):