using System;

using System.Globalization;

using System.Linq;

using System.Net.Http.Headers;

​

public class Program

{   

    public static class AcceptLanguageHandler

    {

        public static readonly CultureInfo[] SupportedCultures = {

                CultureInfo.CreateSpecificCulture("en-GB"),

                CultureInfo.CreateSpecificCulture("nl-BE"),

                CultureInfo.CreateSpecificCulture("fr-BE"),

                CultureInfo.CreateSpecificCulture("fr-LU"),

                CultureInfo.CreateSpecificCulture("nl-NL"),

                CultureInfo.CreateSpecificCulture("de-DE"),

                CultureInfo.CreateSpecificCulture("fi-FI"),

                CultureInfo.CreateSpecificCulture("fr-FR"),

                CultureInfo.CreateSpecificCulture("da-DK"),

                CultureInfo.CreateSpecificCulture("nb-NO"),

                CultureInfo.CreateSpecificCulture("sv-SE"),

                CultureInfo.CreateSpecificCulture("es-ES"),

                CultureInfo.CreateSpecificCulture("ga-IE"),

                CultureInfo.CreateSpecificCulture("en-IE"),

                CultureInfo.CreateSpecificCulture("en-INT"),

                CultureInfo.CreateSpecificCulture("pl-PL"),

                CultureInfo.CreateSpecificCulture("hr-HR")

            };

​

​

        public static CultureInfo Get(System.Net.Http.Headers.StringWithQualityHeaderValue[] AcceptLanguage)

        {

            // get culture by looking at the value with the highest q (or use first supported culture as fallback)

            var culture = AcceptLanguage

                .Where(headerValue => SupportedCultures.Any(c => c.Name == headerValue.Value || c.TwoLetterISOLanguageName == headerValue.Value))

                .OrderByDescending(headerValue => headerValue.Quality ?? 1)

                .Select(headerValue => SupportedCultures.Single(c => c.Name == headerValue.Value || c.TwoLetterISOLanguageName == headerValue.Value))

                .FirstOrDefault() ?? SupportedCultures.First();

​

            return culture;

        }

    }

    public static void Main()

    {

        var nlBe = new StringWithQualityHeaderValue("nl-BE");

        var enGB = new StringWithQualityHeaderValue("en-GB");

        var en = new StringWithQualityHeaderValue("en"); 

        var random = new StringWithQualityHeaderValue("random"); 

        Console.WriteLine(AcceptLanguageHandler.Get([nlBe])); // OK

        Console.WriteLine(AcceptLanguageHandler.Get([nlBe, enGB]));  // OK

        Console.WriteLine(AcceptLanguageHandler.Get([enGB])); // OK

        Console.WriteLine(AcceptLanguageHandler.Get([nlBe, enGB, en])); // OK

        Console.WriteLine(AcceptLanguageHandler.Get([random])); // OK

        Console.WriteLine(AcceptLanguageHandler.Get([en])); // Crashes : Unhandled exception. System.InvalidOperationException: Sequence contains more than one matching element

​

    }

}