[Blazor] Data annotations localization support

[qw-34]

In my case, I have custom localization service (like IStringLocalizer), that retrieve localization from database for user-specific culture. User culture configures in user settings, that may changes in application runtime, i.e. without page reload.

ILocalizationService
{
	string this[string key] { get; }
	string GetString(string key);
	void ChangeLanguage(CultureInfo culture);
}

Service registers as scoped, i.e. each user have own ILocalizationService with own specific culture settings.

services.AddScoped<ILocalizationService, LocalizationService>();

In components this works great, just inject service.

@page "/some-page"
@inject ILocalizationService T
<h1>@T["SomeText"]</h1>

Of course, this does not work in standard case of using data annotation attributes. For example:

User
{
	[Required]
	[Display(Name = "Name")]
	string Name { get; set; }
	
	[Display(Name = "Email")]
	string Email { get; set; }
}

Data annotation attributes can be provided with custom type with localized strings. Something like this:

User
{
	[Required(ErrorMessageResourceName = "Validation_Required", ErrorMessageResourceType = typeof(LocalizationResources))]
	[Display(Name = "Name", ResourceType = typeof(LocalizationResources))]
	string Name { get; set; }
	
	[Display(Name = "Email", ResourceType = typeof(LocalizationResources))]
	string Email { get; set; }
}

LocalizationResources
{
	public static string Name => GetString();
	public static string Email => GetString();
	public static string Validation_Required => GetString();
	
	public static Func<ILocalizationService> LocalizationServiceProvider { get; set; }

	public static string GetString([CallerMemberName] string key = null)
	{
		return LocalizationServiceProvider().GetString(key);
	}
}

Main problem of this approach is that localized strings in LocalizationResources must be as static properties. So we cant directly inject user-specific ILocalizationService. But we can try get user-specific ILocalizationService via Func<ILocalizationService> LocalizationServiceProvider that can be configured, for example, in Configure() method:

public void Configure(IServiceProvider serviceProvider)
{
	LocalizationResources.LocalizationServiceProvider = () => serviceProvider.GetRequiredService<ILocalizationService>();
}

Of course, this does not work, because of scope of serviceProvider in Configure() method differs from user-specific scopes. In order for this approach to work it is necessary in LocalizationResources.LocalizationServiceProvider uses some kind of context that will provide user-scoped IServiceProvider to resolve user-specific ILocalizationService.

So, at this moment, in server-side Blazor is exists any method to localize the data annotation attributes in non-resx scenarios? Have a plan to implement its in future?

[mkArtakMSFT]

Thanks for contacting us, @qw-34.
We don't have any plans to support this in 3.0, but we'll look to bring support for the in the future.

[sven5]

Please also add support for DataAnnotationLocalizerProvider in Blazor - we already have this in MVC.

[agonzalezm]

will this be supported in 3.1? we also need full multi-language support for server-side application texts, data annotations validations, etc

[marinasundstrom]

Localization is now supported in Blazor, usingMicrosoft.AspNetCore.Localization:

builder.Services.AddLocalization();

DataAnnotations are not really supported though.

After some quick investigation, my conclusion is that the DataAnnotationsValidator is the class that should be responsible for resolving the string from the preferred .resx file.

It could be implemented there by injecting StringLocalizer<T>(where T is the Component) into the ``DataAnnotationsValidatorand then pass it to EditContextDataAnnotationsExtensions .AddDataAnnotationsValidation```.

https://github.com/dotnet/aspnetcore/blob/057ec9cfae1831f91f1a0e01397059b20431db7b/src/Components/Forms/src/EditContextDataAnnotationsExtensions.cs

But you need to create adapters to handle the localization of specific data annotations, like in MVC:

https://github.com/dotnet/aspnetcore/tree/c565386a3ed135560bc2e9017aa54a950b4e35dd/src/Mvc/Mvc.DataAnnotations/src

It might be a bigger task than expected.

There is also an experimental ObjectGraphDataAnnotationsValidator that validates not only top-level properties. Maybe that will replace the DataAnnotationsValidator in the future.

[fededim]

Is there any schedule to support Data Annotations localization in Blazor ? Without them Blazor apps are fully localized in a language, but the standard data annotation errors remain still in English....this "double language" is not great from the user perspective. Think about this feature, it's important for every application.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[daniel-scatigno]

With .net Core came the new "way" of Translating strings, using the IStringLocalizer is the new sensation!!
But it came incomplete, it works within MVC and it half works with Blazor. It's a mess in my opinion! This needs to be completed. We need to be able to localize those DataAnnotations Validators message

[ghost]

Thanks for contacting us.

We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[davhdavh]

This belonged in Blazor version 1.0... we are 5 YEARS from that date.

This issue absolutely blocks Blazor from being used for small projects that needs to support a language different than en-US.

On larger projects of-course you can choose shoot yourself in the foot and not use dataannotations, or you can have enough processes in place to make sure that everyone uses your custom dataannotations with your project level translations and have build processes setup to make sure that noone uses the built-in ones, all major undertakings in themselves.

[drlee91]

i'm using mudblazor as designframework, there is alternatively instead of , there dataannotations is done in the razor page, so i could implement formvalidation multilingual for me.. i dont think anything will ever happen here with classic annotations :( maybe u can be inspired ;) https://mudblazor.com/components/form#simple-form-validation

[ghost]

Thanks for contacting us.

We're moving this issue to the .NET 9 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[mduu]

Really? This basic functionality is now laying in your backlog for five years...