Easy Asp.Net Core MVC validation data attributes localization.
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The ForEvolve.AspNetCore.Localization package allows you to enable localization of Asp.Net Core 2.0 applications in a few line of code.

This is very useful for ValidationAttributes like [Required]. No need to specify any string or error message, ForEvolve.AspNetCore.Localization do it for you.


You can:

Install-Package ForEvolve.AspNetCore.Localization


dotnet add package ForEvolve.AspNetCore.Localization

or take a look at https://www.nuget.org/packages/ForEvolve.AspNetCore.Localization/.

Prerelease MyGet

For the pre-release packages, use the ForEvolve NuGet V3 feed URL packages source. See the Table of content project for more info.

Supported languages:

  • English (en)
  • French (fr)
  • Hebrew (he) thanks to aboyaniv
  • Portuguese (pt) thanks to Matheus Avi (Same as pt-BR, needs to be checked)
  • Brazilian portuguese (pt-BR) thanks to Matheus Avi

Supported attributes

  • CompareAttribute
  • EmailAddressAttribute
  • RequiredAttribute
  • CreditCardAttribute
  • FileExtensionsAttribute
  • MaxLengthAttribute
  • MinLengthAttribute
  • PhoneAttribute
  • RangeAttribute
  • RegularExpressionAttribute
  • UrlAttribute
  • StringLengthAttribute (see StringLengthLocalizationValidationAttributeAdapter.cs)

See ForEvolveMvcDefaultLocalizationAdapterOptions.cs for the list of supported attributes used by the DefaultLocalizationValidationAttributeAdapter.

You can also create and register your own adapters and attributes.

How to use

To enable localization for everything, including data annotation, you need to:

  1. Make sure your application is targetting Asp.Net Core 2.0
  2. Add ForEvolve.AspNetCore.Localization NuGet package to your project (or the ForEvolve meta-package).
  3. In Startup.cs add and configure dependencies (see below).
public void ConfigureServices(IServiceCollection services)
    // Localization & options

    // ...

    // MVC

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    // Localization


As you can see, it took only 3 lines of code to enable localization.

Code break down

services.AddForEvolveLocalization(); add all necessary services to the DI container, including supported resources, resource path, etc. This also calls services.AddLocalization(...) for you, defining a default ResourcesPath to "Resources". You can change the default (all defaults actually).

To configure the options, you can pass a second argument of type Action<ForEvolveLocalizationOptions> to the services.AddForEvolveLocalization(); extension method.

To make it easy to use, I made sure that everything is configurable at a single place instead of spreading settings around.

Example 1:

    .AddForEvolveLocalization(options => {
        options.ResourcesPath = "new/place/where/to/store/resources";

Example 2:

    .AddForEvolveLocalization(options => {
        options.ResourcesPath = "new/place/where/to/store/resources";
        options.MvcOptions.EnableViewLocalization = false;
        options.MvcOptions.ConfigureValidationMetadataProvider = (provider) =>
            provider.Adapters.Add(new SomeCoolAdapterThatICreatedOnlyForMyProject());

The IMvcBuilder.AddForEvolveMvcLocalization(); extension method register the ILocalizationValidationMetadataProvider (this does the validation attribute localization magic) as well as AddViewLocalization() and AddDataAnnotationsLocalization().

You can opt-out by setting options.MvcOptions.EnableViewLocalization or options.MvcOptions.EnableDataAnnotationsLocalization to false (in the call to services.AddForEvolveLocalization();).

The IApplicationBuilder.UseForEvolveRequestLocalization() extension method calls app.UseRequestLocalization() with some options. Once again all parameters are updatable in the initial call to services.AddForEvolveLocalization();.

How to contribute a translation

Since I only know French and English, I can't translate messages into more languages, so contributions are very welcome.

How to submit a new translation:

  1. Fork the repo
  2. Create a resource file for the language you want to translate error messages into.
  3. Translate it (obviously)
  4. Add the new language to the Supported languages section of the README.md file with a "thanks to you" attribution and link
  5. Open a pull request

Since I don't speak all languages, I cannot validate those that I don't know (except maybe by using Google Translate), so it's up to you to makes things right! (or PR corrections)

I will do my best to integrates PR as fast as possible.

Where are the error messages located?

If you look under src/ForEvolve.AspNetCore.Localization/Resources/, you will find DataAnnotationSharedResource.resx and DataAnnotationSharedResource.{lang}.resx files. You can copy any one of those and translate the values.

If you want to create a culture-specific translation, example: fr-CA, please make sure that there is an fr translation (neutral culture) first which will be the default for that language.


  • First we need a DataAnnotationSharedResource.fr.resx file (already there).
  • Then we could add DataAnnotationSharedResource.fr-CA.resx, DataAnnotationSharedResource.fr-FR.resx, etc.

Error messages

I modified default error messages a little to make them more linear. Sometimes it was written The field {0} ... and sometimes it was The {0} field .... I decided to normalize messages to The {0} field ....

I am open to suggestion if you think this makes no sense. English is only my secondary language.

Error messages source (if you want the original error messages): corefx/src/System.ComponentModel.Annotations/src/Resources/Strings.resx

The plan

Before looking to the future let's look at the history of the project.

The history of the project

I created this project because I did not want to code something similar to this every single time I start a new Asp.Net Core application. I did not want to write an error message on every ValidationAttribute either (which seems to be the official solution).

To be honest, I was a little disappointed to see how hard it is to localize Asp.Net Core validation attributes. This should be trivial.

I don't want to criticize the design made by the team that built that without knowing, so I will assume there are some good reasons behind these design choices (technical or not).

That said, the other parts of the localization pipeline of Asp.Net Core are pretty neat with IStringLocalizer, IHtmlLocalizer and IViewLocalizer.

The future

I plan on using this library for multiple projects so it should evolve in the future. If you have ideas, requests or find bugs, feel free to open issues or submit PRs.

If you want to contributes some code, other than translating error messages, feel free to contact me.

To conclude, I hope this is only the beginning of the project.

For example, I'd like, at some point, to extract the resources somewhere else, maybe use some other resource provider like a database or JSON files...