"FormattableString"

static void Test() {
	var percentageComplete = 12.345d;
	FormattableString str = $"Percentage complete: {percentageComplete:F2}%";

	Console.WriteLine(str.ToString(CultureInfo.GetCultureInfo("de-DE"))); // Prints "Percentage complete: 12,35%" (German-style number formatting)
}


Code snippet taken from "Two Decades of C#: A Reference - C# 5 and C# 6".