Languages and custom texts

Choose the language

The texts are included in Dutch, English, French, German, Italian, Japanese, Korean, Portuguese, Simplified Chinese, Spanish and Turkish. Pass the culture to ToString:

var timeProvider = new FakeTimeProvider(new DateTimeOffset(2024, 6, 15, 12, 0, 0, TimeSpan.Zero));
var date = RelativeDate.Get(timeProvider.GetUtcNow().AddDays(-3), timeProvider);

Assert.Equal("3 days ago", date.ToString(format: null, CultureInfo.GetCultureInfo("en-US")));
Assert.Equal("il y a 3 jours", date.ToString(format: null, CultureInfo.GetCultureInfo("fr-FR")));
Assert.Equal("vor 3 Tagen", date.ToString(format: null, CultureInfo.GetCultureInfo("de")));
Assert.Equal("hace 3 días", date.ToString(format: null, CultureInfo.GetCultureInfo("es")));

// A language without translations uses the English texts
Assert.Equal("3 days ago", date.ToString(format: null, CultureInfo.GetCultureInfo("sv-SE")));

// string.Format and interpolated strings pass their culture to RelativeDate
Assert.Equal("Modifié il y a 3 jours", string.Create(CultureInfo.GetCultureInfo("fr-FR"), $"Modifié {date}"));

• A specific culture uses the texts of its language: fr-FR and fr-CA use the French texts.
• A culture without texts uses the English ones, as does the invariant culture.
• Without a culture, the text uses CultureInfo.CurrentUICulture. In ASP.NET Core, the request localization middleware sets it for each request.
• The format provider can be a CultureInfo, or any IFormatProvider that returns a CultureInfo from GetFormat(typeof(CultureInfo)).

The translations are .NET satellite resource assemblies. If your project sets the SatelliteResourceLanguages MSBuild property to keep only some languages, add the languages you display, or they fall back to English.

Change the texts

The texts come from LocalizationProvider.Current, an ILocalizationProvider used by every RelativeDate. Its GetString(name, culture) method returns the text of a resource for a culture.

To change some texts, write a provider that returns your texts and asks the previous provider for the others:

private sealed class CasualEnglishLocalizationProvider(ILocalizationProvider inner) : ILocalizationProvider
{
    public string GetString(string name, CultureInfo? culture)
    {
        var text = (culture?.TwoLetterISOLanguageName, name) switch
        {
            ("en", "Now") => "just now",
            ("en", "OneSecondAgo" or "ManySecondsAgo") => "a few seconds ago",
            _ => null,
        };

        return text ?? inner.GetString(name, culture);
    }
}

Set it once, at the start of the application:

// Wrap the current provider, so the built-in texts stay available
LocalizationProvider.Current = new CasualEnglishLocalizationProvider(LocalizationProvider.Current);

var timeProvider = new FakeTimeProvider(new DateTimeOffset(2024, 6, 15, 12, 0, 0, TimeSpan.Zero));
var date = RelativeDate.Get(timeProvider.GetUtcNow().AddSeconds(-20), timeProvider);

Assert.Equal("a few seconds ago", date.ToString(format: null, CultureInfo.GetCultureInfo("en-US")));
Assert.Equal("il y a 20 secondes", date.ToString(format: null, CultureInfo.GetCultureInfo("fr-FR")));

LocalizationProvider.Current is global, and setting it to null throws an ArgumentNullException. Keep the previous provider to restore it: the built-in provider is not public, so LocalizationProvider.Current, read before you replace it, is the only way to reach it. In tests that change the provider, restore it in a finally block and do not run these tests in parallel with the others.

The same approach adds a language: return your translations when culture is that language, and the previous provider's texts otherwise.

Resource names

{0} is replaced by the number, formatted with the culture. A text without {0} is used as is.