How to Localize validation message (DataAnnotationsValidator) in blazor server side

Here is my solution for localizing data annotation error messages. I create two resource files, one for fields and another one for error messages.

  • DisplayNameResource for localizing fields
  • ErrorMessageResource for localizing error messages

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In view model class use Display attribute for localizing field name. To specify resource file use ResourceType property on Display attribute:

[Display(Name = "Address", ResourceType = typeof(DisplayNameResource))]

And on validation attributes use ErrorMessageResourceName and ErrorMessageResourceType to specify resource file:

[Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]

Here is full example:

public class SomeViewModel
{
    [Display(Name = "Address", ResourceType = typeof(DisplayNameResource))]
    [Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    [StringLength(256, ErrorMessageResourceName = "MaxLengthError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    public string Address { get; set; }

    [Display(Name = "Phone", ResourceType = typeof(DisplayNameResource))]
    [Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    [RegularExpression("^09([0-9]{9})$", ErrorMessageResourceName = "PhoneLengthError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    public string Phone { get; set; }

    [Display(Name = "Password", ResourceType = typeof(DisplayNameResource))]
    [Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    [StringLength(50, MinimumLength = 6, ErrorMessageResourceType = typeof(ErrorMessageResource), ErrorMessageResourceName = "MinxMaxLengthError")]
    public string Password { get; set; }

    [Display(Name = "ConfirmPassword", ResourceType = typeof(DisplayNameResource))]
    [Required(ErrorMessageResourceName = "RequiredError", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    [StringLength(50, MinimumLength = 6, ErrorMessageResourceType = typeof(ErrorMessageResource), ErrorMessageResourceName = "MinxMaxLengthError")]
    [Compare("Password", ErrorMessageResourceName = "PasswordConfirmMisMatch", ErrorMessageResourceType = typeof(ErrorMessageResource))]
    public string ConfirmPassword { get; set; }
}

Error message for MaxLengthError is {0} cannot be longer than {1} character, so {0} will be replaced with localized filed name and {1} will be replaced with the 256 you specified on attribute [StringLength(256,...