using System;

using System.Linq;

using System.Collections.Generic;

using System.Net.Http.Headers;

​

public class Program

{

    public static void Main()

    {

        Test("fr,fr-FR;q=0.8,;q=0.9,en;q=0.7,en-US;q=0.6");

        Test("pt-PT,pt;q=0.9,en;q=0.8,en-CA;q=0.7,fr-CA;q=0.6,fr;q=0.5,tr;q=0.4,fr-FR;q=0.3,uk;q=0.2,en-GB;q=0.1,en-US;q=0.1,pt-BR;q=0.1");

    }

    public static void Test(string acceptLanguageHeaderValue)

    {

        Console.WriteLine($"Header: {acceptLanguageHeaderValue}");

        var acceptedLanguages = ParseAcceptLanguageHeader(acceptLanguageHeaderValue);

​

        foreach (var lang in acceptedLanguages)

        {

            Console.WriteLine($"  {lang.Value} => {lang.Quality}");

        }

        Console.WriteLine();

    }

​

    public static IEnumerable<StringWithQualityHeaderValue> ParseAcceptLanguageHeader(string acceptLanguageHeaderValue)

    {

        return acceptLanguageHeaderValue

            .Split(',')

            .Select(rawValue => StringWithQualityHeaderValue.TryParse(rawValue, out var parsed) ? parsed : null)

            .OfType<StringWithQualityHeaderValue>()

            .OrderByDescending(lang => lang.Quality ?? 1.0);

    }

}