How to localize error messages in .NET Core 6

Question

I am new to .NET Core 6 and I have realized that several things should be done manually.

One of them is localization. For example, when using a simple action to change the user password, the message "Incorrect password." is returned in the errors collection when the old password mismatch.

I have spent a lot of time trying to localize that simple message so that it is shown in Spanish. I have read a lot of pages telling about this but none works. I think it is because this message is not a DataAnnotation message.

When I used .NET Framework, all of these were made automatically since the resource DLL is always installed by default. It seems that in .NET Core 6 those DLL's are missing, or at least, they are vey hidden.

As an attempt, I added this to Program.cs file:

builder.Services.AddMvc()
    .AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix, options => options.ResourcesPath = "Resources")
    .AddDataAnnotationsLocalization();

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

builder.Services.Configure<RequestLocalizationOptions>(options =>
{
    var supportedCultures = new[] { new CultureInfo("en"), new CultureInfo("es") };
    options.DefaultRequestCulture = new RequestCulture("es");
    options.SupportedCultures = supportedCultures;
    options.SupportedUICultures = supportedCultures;
});

app.UseRequestLocalization();

And also added a file "Resouces\ErrorMessages.es.resx" with an entry whose key is PasswordMismatch with the message in Spanish, but no avail.

Any help, please?

Answer 1

Alought I couldn't check the details of your resourcefile,I think there's something wrong with your resourcefile for the name you've shown

Resouces\ErrorMessages.es.resx

I tried in my case as below:

public class TestModel
    {
        
        [Required(ErrorMessage = "The Email field is required.")]
        [EmailAddress(ErrorMessage = "The Email field is not a valid email address.")]
        [Display(Name = "Email")]
        public string Email { get; set; }

        [Required(ErrorMessage = "The Password field is required.")]
        [StringLength(8, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
        [DataType(DataType.Password)]
        [Display(Name = "Password")]
        public string Password { get; set; }

        [DataType(DataType.Password)]
        [Display(Name = "Confirm password")]
        [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
        public string ConfirmPassword { get; set; }
    }

in Razor View:

<div class="row">
    <div class="col-md-4">
        <form asp-action="Create">
            <div asp-validation-summary="ModelOnly" class="text-danger"></div>
            <div class="form-group">
                <label asp-for="Email" class="control-label"></label>
                <input asp-for="Email" class="form-control" />
                <span asp-validation-for="Email" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="Password" class="control-label"></label>
                <input asp-for="Password" class="form-control" />
                <span asp-validation-for="Password" class="text-danger"></span>
            </div>
            <div class="form-group">
                <label asp-for="ConfirmPassword" class="control-label"></label>
                <input asp-for="ConfirmPassword" class="form-control" />
                <span asp-validation-for="ConfirmPassword" class="text-danger"></span>
            </div>
            <div class="form-group">
                <input type="submit" value="Create" class="btn btn-primary" />
            </div>
        </form>
    </div>
</div>

It works well:

Update：

Since You are not interested in developing a multilingual site,I think the most simlpe solution is Custom an Attribute as below:

public class CusRequiredAttribute: RequiredAttribute
    {
        public CusRequiredAttribute()
        {
            //You could wrote the errormessage in your language as well
            ErrorMessage = "{0}Required";
        }
    }

add [CusRequired]attrbute on the target property

for developing a multilingual site

Create an empty class named SharedResources and a resource file as below:

set as below in startup:

services.AddControllersWithViews()
                .AddDataAnnotationsLocalization(
                options =>
                {
                    options.DataAnnotationLocalizerProvider = (type, factory) =>
                        factory.Create(typeof(SharedResources));
                });

Result:

Answer 2

A hint: if the problem is with the PasswordValidator (it wasn't getting the translated messages from the resource file), you can do it (in .NET 7, at least):

var passwordValidator = new PasswordValidator<ApplicationUser>(new LocalizedIdentityErrorDescriber());

And the LocalizedIdentityErrorDescriber is defined here: https://stackoverflow.com/a/53587825/1673326

If anyone needs the pt-BR translated messages, here they are: https://drive.google.com/file/d/1lNu6YjsGvJto4_fCg6MtdIE6vZrldKkC/view?usp=sharing