How can ASP.NET Core model binding error messages be localized?

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ASP.NET Core offers various mechanisms for localizing error messages related to model binding. Here are some of the ways:

1. Using data annotations: ASP.NET Core offers data annotations to decorate model properties with attributes that provide validation rules. These attributes have a parameter named "ErrorMessage" that can be used to provide localized error messages. For example:

public class MyViewModel
{
    [Required(ErrorMessage = "This field is required.")]
    [StringLength(50, ErrorMessage = "The field {0} must be a string with a minimum length of {2} and a maximum length of {1}.", MinimumLength = 5)]
    public string Name { get; set; }
}

In the above code, "ErrorMessage" parameter is used to provide localized error messages for "Required" and "StringLength" attributes.

1. Adding resources: ASP.NET Core allows adding localized resources for various languages using the "ResourceManager" class. These resources can be added as .resx files and used to provide localized error messages for model binding. For example:

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

In the above code, "AddDataAnnotationsLocalization" method is used to register a data annotations localization provider that uses "MyResource" class to provide localized error messages.

1. Customizing the error message provider: ASP.NET Core also allows customizing the error message provider to provide localized error messages. To customize the error message provider, you can create a class that implements the "IModelBindingMessageProvider" interface and register it using the "AddMvcOptions" method. For example:

services.AddMvc(options =>
{
    options.ModelBindingMessageProvider.SetValueMustNotBeNullAccessor(
        (value) => "This field is required.");
})

In the above code, "SetValueMustNotBeNullAccessor" method is used to set a custom error message for when a required value is not provided.