LanguageProvider

Decides which languages a request wants. The default implementation reads the Accept-Language header, falling back to DefaultLanguage from LocalizationSettings when the header is absent or contains no well-formed language tag. AddMessageLocalization registers that default only when nothing has claimed ILanguageProvider yet, so register a custom provider before that call and it is kept.

GetLanguage

Returns the single best language for the current request, ignoring any lower-ranked alternative the caller would accept. Never blank: with nothing to negotiate from it returns the configured default, since the result is looked up as-is.

using System.Globalization;
using AlmightyShogun.AspNet.Localization;

public sealed class CurrencyFormatter(ILanguageProvider languageProvider)
{
    public string Format(decimal amount) => amount.ToString(
        "C",
        new CultureInfo(languageProvider.GetLanguage())
    );
}

WARNING

The returned value is used as a directory name when message files are resolved, so the message provider accepts only a well-formed language tag: two or three letters, then any number of - separated parts of two to eight letters or digits. A replacement implementation that returns raw user input therefore resolves no messages at all rather than reading elsewhere on disk.

Type signature

public string GetLanguage();

GetLanguages

Returns every language the caller accepts, in preference order, so MessageResolver can try a lower-ranked language before falling back to the configured default. Never empty, and a provider with nothing to rank returns a single entry.

It has a default implementation returning just GetLanguage(), so a custom provider that only knows one language implements GetLanguage alone and inherits this.

using AlmightyShogun.AspNet.Localization;

public sealed class ArticleService(ILanguageProvider languageProvider)
{
    public string? FindBestTranslation(
        IReadOnlyDictionary<string, string> byLanguage
    ) => languageProvider.GetLanguages()
            .Select(language => byLanguage.GetValueOrDefault(language))
            .FirstOrDefault(translation => translation != null);
}

Type signature

public IReadOnlyList<string> GetLanguages() => [GetLanguage()];