Nested Localization

When a localizable type has a property that is itself ILocalizable, the formatter recurses automatically — each nested value goes through the full resolution chain.

Example: Payment Validation

Define two error types where one references the other:

public class InvalidCurrencyError(string currencyCode) : ILocalizable
{
    public string CurrencyCode { get; } = currencyCode;
}

public class PaymentValidationError(
    string fieldName,
    InvalidCurrencyError detail) : ILocalizable
{
    public string FieldName { get; } = fieldName;
    public InvalidCurrencyError Detail { get; } = detail;
}

Register templates in your JSON resource:

{
  "MyApp.InvalidCurrencyError": "'{CurrencyCode}' is not a valid currency",
  "MyApp.PaymentValidationError": "Payment field '{FieldName}' is invalid: {Detail}"
}

Format the outer error:

var error = new PaymentValidationError("Amount", new InvalidCurrencyError("XYZ"));
var message = formatter.Format(error);
// -> "Payment field 'Amount' is invalid: 'XYZ' is not a valid currency"

The {Detail} placeholder is resolved by formatting the nested InvalidCurrencyError through the same resolution chain.

How It Works

When the formatter encounters a {PropertyName} placeholder whose value implements ILocalizable, it calls Format() recursively instead of ToString(). The full resolution chain applies to each nested value:

1. Self-provider (ILocalizationProvider)
2. DI provider (ILocalizationProvider<T>)
3. Registry template
4. Fallback (TypeName(Prop=val))

Fallback Behavior

If the inner type has no template, the fallback representation is used:

// No template registered for InvalidCurrencyError
formatter.Format(error);
// -> "Payment field 'Amount' is invalid: InvalidCurrencyError(CurrencyCode=XYZ)"

The fallback itself also recurses — if a fallback property is ILocalizable, it gets formatted through the resolution chain too.

Culture propagation

Culture is propagated through the entire nesting chain. A single Format(error, culture) call ensures every nested ILocalizable is formatted with the same culture.

Related

Provider Chain The four-step resolution order applied at each nesting level

Localizable Types Define types that participate in nested localization

JSON Serialization Nested ILocalizable properties are also handled during serialization