BrowserLanguageResolver.cs

using System.Collections.Generic;
using System.Linq;
using Sitecore.Configuration;
using Sitecore.Data.Managers;
using Sitecore.Diagnostics;
using Sitecore.Globalization;
using Sitecore.Pipelines.HttpRequest;
using Sitecore.Web;
using Sitecore.Sites;

namespace Sitecore.Foundation.Multisite.Pipelines.HttpRequestBegin
{
    /***
     * 1) Register this processor in config:
     *     <pipelines>
     *          <httpRequestBegin>
     *              <processor patch:after="*[@type='Sitecore.Pipelines.HttpRequest.LanguageResolver, Sitecore.Kernel']"
     *                  type="Sitecore.Foundation.Multisite.Pipelines.HttpRequestBegin.BrowserLanguageResolver, Sitecore.Foundation.Multisite" />
     *          </httpRequestBegin>
     *      </pipelines>
     *
     * 2) Mark all your sites which you want this processor be executed:
     *    <site name="myCustomSite" patch:before="site[@name='website']"
     *      ...
     *      isBrowserLanguageResolving="true" />
     *
     * 3) Optional: Implement method "IsLanguageConfigured". This should check if the resolved language is used on the current site
     *
     */
    public class BrowserLanguageResolver : HttpRequestProcessor
    {
        public override void Process(HttpRequestArgs args)
        {
            // Check setting
            if (!IsBrowserLanguageDetectionEnabled())
            {
                return;
            }

            // Site couldn't be resolved
            var site = Context.Site;
            if (site == null)
            {
                return;
            }

            // Only execute this processor on custom sites
            if (IsCustomSite(Context.Site))
            {
                return;
            }

            // Check for Database
            if (Context.Database == null)
            {
                return;
            }

            // Cookie already set
            var languageFromCookie = WebUtil.GetCookieValue(site.GetCookieKey("lang"));
            if (!string.IsNullOrEmpty(languageFromCookie))
            {
                return;
            }

            // Try to get browser language
            var language = GetBrowserLanguage(args);
            if (language == null)
            {
                return;
            }

            // Optional: Check if the resolved language is used on the current site
            if (!IsLanguageConfigured(language))
            {
                return;
            }

            Context.Language = language;
            Tracer.Info("Language changed to \"" + language.Name + "\" due to the browser language of the current request.");
        }

        protected virtual bool IsCustomSite(SiteContext site)
        {
            if (site == null)
            {
                return false;
            }

            if (!bool.TryParse(site.Properties["isBrowserLanguageResolving"], out var isWebSite))
            {
                return false;
            }

            return isWebSite;
        }

        protected virtual bool IsLanguageConfigured(Language language)
        {
            // TODO (optional): Add logic here which checks if the resolved language is used on the current site
            return true;
        }

        protected virtual bool IsBrowserLanguageDetectionEnabled()
        {
            return Settings.GetBoolSetting("Sitecore.Foundation.Multisite.BrowserLanguageResolver.IsEnabled", true);
        }

        protected virtual Language GetBrowserLanguage(HttpRequestArgs args)
        {
            var browserLanguages = GetBrowserLanguageStrings(args);

            foreach (var browserLanguage in browserLanguages)
            {
                if (string.IsNullOrEmpty(browserLanguage))
                {
                    continue;
                }

                var language = LanguageManager.GetLanguage(browserLanguage, Context.Database);
                if (language != null)
                {
                    return language;
                }
            }

            return null;
        }

        protected virtual IEnumerable<string> GetBrowserLanguageStrings(HttpRequestArgs args)
        {
            var languages = new List<string>();

            if (args.HttpContext.Request.UserLanguages == null)
            {
                return languages;
            }
            
            var fullLanguage = args.HttpContext.Request.UserLanguages[0];
            if (string.IsNullOrEmpty(fullLanguage))
            {
                return languages;
            }

            // Add culture code
            var mainLanguage = fullLanguage.Split(';').FirstOrDefault();
            if (string.IsNullOrEmpty(mainLanguage))
            {
                return languages;
            }

            languages.Add(mainLanguage);

            // Add 2-char ISO code. This is especially usefull if you are using 2-char languages in Sitecore.
            var isoArray = mainLanguage.Split('-');
            if (isoArray.Length == 2)
            {
                languages.Add(isoArray[0]);
            }

            return languages;
        }
    }
}