MessageResolver

Resolves localized messages from the JSON message files described on the localization page. Application code depends on IMessageResolver. Resolution never fails: a key the negotiated language does not define is returned as itself, so a missing translation degrades to a readable identifier instead of an exception or a blank body.

Resolve

Resolves a message key, optionally formatting it with parameters. Parameters are substituted with string.Format, so the template uses {0}, {1}, and so on. They are formatted in the culture of the language the message resolved in, so a number in a Dutch message reads 1234,56 rather than taking the server's culture.

The language is negotiated once through ResolveLanguage and every key comes from that one language, so a key it does not define comes back as itself rather than being looked up in the next accepted language.

A template whose placeholders do not match the supplied parameters returns the raw template rather than throwing, so a bad message file cannot fail a request.

OrdersController.cs

using Microsoft.AspNetCore.Mvc;
using AlmightyShogun.AspNet.Localization;

[ApiController]
[Route("orders")]
public sealed class OrdersController(
    IMessageResolver messageResolver
) : ControllerBase
{
    [HttpGet("{id:int}")]
    public IActionResult Get(int id)
    {
        Order? order = FindOrder(id);

        return order is null
            ? NotFound(messageResolver.Resolve("orders.not-found", [id]))
            : Ok(order);
    }

    [HttpDelete("{id:int}")]
    public IActionResult Delete(int id)
        => BadRequest(messageResolver.Resolve("orders.read-only"));
}

messages/en/orders.json

{
    "not-found": "Order {0} does not exist",
    "read-only": "Orders cannot be deleted"
}

Type signature

public string Resolve(string key);

public string Resolve(string key, IReadOnlyList<object?> parameters);

ResolveLanguage

Returns the language messages are currently being served in: the first candidate in the negotiation chain whose directory holds any messages, or DefaultLanguage when none does. This is what Resolve reads from and what the middleware writes to the response Content-Language header.

Useful when a response needs to state its own language, for example an email body rendered from the same message files.

using AlmightyShogun.AspNet.Localization;

string language = messageResolver.ResolveLanguage();

Type signature

public string ResolveLanguage();