ASP.Net Core localization

Question

ASP.Net core features new support for localization.

In my project I need only one language. For most of the text and annotations I can specify things in my language, but for text coming from ASP.Net Core itself the language is English.

Examples:

• Passwords must have at least one uppercase ('A'-'Z').
• Passwords must have at least one digit ('0'-'9').
• User name '[e-mail]' is already taken.
• The E-post field is not a valid e-mail address.
• The value '' is invalid.

I've tried setting the culture manually, but the language is still English.

app.UseRequestLocalization(new RequestLocalizationOptions
{
    DefaultRequestCulture = new RequestCulture("nb-NO"),
    SupportedCultures = new List<CultureInfo> { new CultureInfo("nb-NO") },
    SupportedUICultures = new List<CultureInfo> { new CultureInfo("nb-NO") }
});

How can I change the language of ASP.Net Core, or override its default text?

Answer 1

For those who are wondering, if it is possible to localize the messages for currently chosen culture, yes it is possible. In asp.net core 2.2 you can create a class LocalizedIdentityErrorDescriber where IdentityResources is the name of your dummy class (it is described here: Globalization and localization):

public class LocalizedIdentityErrorDescriber : IdentityErrorDescriber
{
    /// <summary> 
    /// The <see cref="IStringLocalizer{LocalizedIdentityErrorDescriber}"/>
    /// used to localize the strings
    /// </summary>
    private readonly IStringLocalizer<IdentityResources> localizer;

    /// <summary>
    /// Initializes a new instance of the <see cref="LocalizedIdentityErrorDescriber"/> class.
    /// </summary>
    /// <param name="localizer">
    /// The <see cref="IStringLocalizer{LocalizedIdentityErrorDescriber}"/>
    /// that we will use to localize the strings
    /// </param>
    public LocalizedIdentityErrorDescriber(IStringLocalizer<IdentityResources> localizer)
    {
        this.localizer = localizer;
    }

    /// <summary>
    /// Returns the default <see cref="IdentityError" />.
    /// </summary>
    /// <returns>The default <see cref="IdentityError" /></returns>
    public override IdentityError DefaultError()
    {
        return this.GetErrorByCode(nameof(DefaultError));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a concurrency failure.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating a concurrency failure.</returns>
    public override IdentityError ConcurrencyFailure()
    {
        return this.GetErrorByCode(nameof(ConcurrencyFailure));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a password mismatch.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating a password mismatch.</returns>
    public override IdentityError PasswordMismatch()
    {
        return this.GetErrorByCode(nameof(PasswordMismatch));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating an invalid token.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating an invalid token.</returns>
    public override IdentityError InvalidToken()
    {
        return this.GetErrorByCode(nameof(InvalidToken));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating an external login is already associated with an account.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating an external login is already associated with an account.</returns>
    public override IdentityError LoginAlreadyAssociated()
    {
        return this.GetErrorByCode(nameof(LoginAlreadyAssociated));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating the specified user <paramref name="userName" /> is invalid.
    /// </summary>
    /// <param name="userName">The user name that is invalid.</param>
    /// <returns>An <see cref="IdentityError" /> indicating the specified user <paramref name="userName" /> is invalid.</returns>
    public override IdentityError InvalidUserName(string userName)
    {
        return this.FormatErrorByCode(nameof(InvalidUserName), (object)userName);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating the specified <paramref name="email" /> is invalid.
    /// </summary>
    /// <param name="email">The email that is invalid.</param>
    /// <returns>An <see cref="IdentityError" /> indicating the specified <paramref name="email" /> is invalid.</returns>
    public override IdentityError InvalidEmail(string email)
    {
        return this.FormatErrorByCode(nameof(InvalidEmail), (object)email);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating the specified <paramref name="userName" /> already exists.
    /// </summary>
    /// <param name="userName">The user name that already exists.</param>
    /// <returns>An <see cref="IdentityError" /> indicating the specified <paramref name="userName" /> already exists.</returns>
    public override IdentityError DuplicateUserName(string userName)
    {
        return this.FormatErrorByCode(nameof(DuplicateUserName), (object)userName);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating the specified <paramref name="email" /> is already associated with an account.
    /// </summary>
    /// <param name="email">The email that is already associated with an account.</param>
    /// <returns>An <see cref="IdentityError" /> indicating the specified <paramref name="email" /> is already associated with an account.</returns>
    public override IdentityError DuplicateEmail(string email)
    {
        return this.FormatErrorByCode(nameof(DuplicateEmail), (object)email);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating the specified <paramref name="role" /> name is invalid.
    /// </summary>
    /// <param name="role">The invalid role.</param>
    /// <returns>An <see cref="IdentityError" /> indicating the specific role <paramref name="role" /> name is invalid.</returns>
    public override IdentityError InvalidRoleName(string role)
    {
        return this.FormatErrorByCode(nameof(InvalidRoleName), (object)role);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating the specified <paramref name="role" /> name already exists.
    /// </summary>
    /// <param name="role">The duplicate role.</param>
    /// <returns>An <see cref="IdentityError" /> indicating the specific role <paramref name="role" /> name already exists.</returns>
    public override IdentityError DuplicateRoleName(string role)
    {
        return this.FormatErrorByCode(nameof(DuplicateRoleName), (object)role);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a user already has a password.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating a user already has a password.</returns>
    public override IdentityError UserAlreadyHasPassword()
    {
        return this.GetErrorByCode(nameof(UserAlreadyHasPassword));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating user lockout is not enabled.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating user lockout is not enabled..</returns>
    public override IdentityError UserLockoutNotEnabled()
    {
        return this.GetErrorByCode(nameof(UserLockoutNotEnabled));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a user is already in the specified <paramref name="role" />.
    /// </summary>
    /// <param name="role">The duplicate role.</param>
    /// <returns>An <see cref="IdentityError" /> indicating a user is already in the specified <paramref name="role" />.</returns>
    public override IdentityError UserAlreadyInRole(string role)
    {
        return this.FormatErrorByCode(nameof(UserAlreadyInRole), (object)role);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a user is not in the specified <paramref name="role" />.
    /// </summary>
    /// <param name="role">The duplicate role.</param>
    /// <returns>An <see cref="IdentityError" /> indicating a user is not in the specified <paramref name="role" />.</returns>
    public override IdentityError UserNotInRole(string role)
    {
        return this.FormatErrorByCode(nameof(UserNotInRole), (object)role);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a password of the specified <paramref name="length" /> does not meet the minimum length requirements.
    /// </summary>
    /// <param name="length">The length that is not long enough.</param>
    /// <returns>An <see cref="IdentityError" /> indicating a password of the specified <paramref name="length" /> does not meet the minimum length requirements.</returns>
    public override IdentityError PasswordTooShort(int length)
    {
        return this.FormatErrorByCode(nameof(PasswordTooShort), (object)length);
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a password entered does not contain a non-alphanumeric character, which is required by the password policy.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating a password entered does not contain a non-alphanumeric character.</returns>
    public override IdentityError PasswordRequiresNonAlphanumeric()
    {
        return this.GetErrorByCode(nameof(PasswordRequiresNonAlphanumeric));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a password entered does not contain a numeric character, which is required by the password policy.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating a password entered does not contain a numeric character.</returns>
    public override IdentityError PasswordRequiresDigit()
    {
        return this.GetErrorByCode(nameof(PasswordRequiresDigit));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a password entered does not contain a lower case letter, which is required by the password policy.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating a password entered does not contain a lower case letter.</returns>
    public override IdentityError PasswordRequiresLower()
    {
        return this.GetErrorByCode(nameof(PasswordRequiresLower));
    }

    /// <summary>
    /// Returns an <see cref="IdentityError" /> indicating a password entered does not contain an upper case letter, which is required by the password policy.
    /// </summary>
    /// <returns>An <see cref="IdentityError" /> indicating a password entered does not contain an upper case letter.</returns>
    public override IdentityError PasswordRequiresUpper()
    {
        return this.GetErrorByCode(nameof(PasswordRequiresUpper));
    }

    public override IdentityError PasswordRequiresUniqueChars(int uniqueChars)
    {
        return this.FormatErrorByCode(nameof(PasswordRequiresUniqueChars), (object)uniqueChars);
    }

    public override IdentityError RecoveryCodeRedemptionFailed()
    {
        return this.GetErrorByCode(nameof(RecoveryCodeRedemptionFailed));
    }

    /// <summary>Returns a localized <see cref="IdentityError"/> for the provided code.</summary>
    /// <param name="code">The error's code.</param>
    /// <returns>A localized <see cref="IdentityError"/>.</returns>
    private IdentityError GetErrorByCode(string code)
    {
        return new IdentityError()
        {
            Code = code,
            Description = this.localizer.GetString(code)
        };
    }

    /// <summary>Formats a localized <see cref="IdentityError"/> for the provided code.</summary>
    /// <param name="code">The error's code.</param>
    /// <param name="parameters">The parameters to format the string with.</param>
    /// <returns>A localized <see cref="IdentityError"/>.</returns>
    private IdentityError FormatErrorByCode(string code, params object[] parameters)
    {
        return new IdentityError
        {
            Code = code,
            Description = string.Format(this.localizer.GetString(code, parameters))
        };
    }
}

Then create resource files for your languages as followed: Resources\(name of dummy class described above)(.culture).resx. For your default language culture should be left blank. And don't forget about the "." before culture name if it is not default. Your IdentityResources files should look like this:

In Startup.cs add the following lines:

 public void ConfigureServices(IServiceCollection services)
 {
      services.AddLocalization(opts => { opts.ResourcesPath = "Resources"; });
      services.AddIdentity<IdentityUser, IdentityRole>()
           .AddEntityFrameworkStores<nameofyourdbcontext>()
           .AddDefaultTokenProviders()
           .AddErrorDescriber<LocalizedIdentityErrorDescriber>(); // this line is important
       services.Configure<RequestLocalizationOptions>(options =>
       {
            var supportedCultures = new[]
            {
                new CultureInfo("en"), // english
                new CultureInfo("tr"), // turkish
                new CultureInfo("ru")  // russian
            };

            options.DefaultRequestCulture = new RequestCulture(culture: "en", uiCulture: "en");
            options.SupportedCultures = supportedCultures;
            options.SupportedUICultures = supportedCultures;
            options.RequestCultureProviders.Insert(0, new CookieRequestCultureProvider()); // type of CultureProvider you want.
        });
 }
 public void Configure(IApplicationBuilder app, IHostingEnvironment env)
 {
        var localizationOptions = app.ApplicationServices.GetService<IOptions<RequestLocalizationOptions>>();
        // IT IS IMPORTANT TO CALL UseRequestLocalization BEFORE UseMvc
        app.UseRequestLocalization(localizationOptions.Value);
        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}"
            );
        });
 }

By now you are almost done but you will need to set Culture cookie and there is a code example in here: Globalization and localization. Hope it helps someone.