Umbraco-CMS/src/Umbraco.Web.Common/Localization/UmbracoPublishedContentCultureProvider.cs

using System;
using System.Globalization;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Localization;
using Microsoft.Extensions.Primitives;
using Umbraco.Cms.Core.Routing;
using Umbraco.Cms.Web.Common.Routing;

namespace Umbraco.Cms.Web.Common.Localization
{
    /// <summary>
    /// Sets the request culture to the culture of the <see cref="IPublishedRequest"/> if one is found in the request
    /// </summary>
    public class UmbracoPublishedContentCultureProvider : RequestCultureProvider
    {
        private readonly RequestLocalizationOptions _localizationOptions;
        private readonly object _locker = new object();

        /// <summary>
        /// Initializes a new instance of the <see cref="UmbracoPublishedContentCultureProvider"/> class.
        /// </summary>
        public UmbracoPublishedContentCultureProvider(RequestLocalizationOptions localizationOptions) => _localizationOptions = localizationOptions;

        /// <inheritdoc/>
        public override Task<ProviderCultureResult> DetermineProviderCultureResult(HttpContext httpContext)
        {
            UmbracoRouteValues routeValues = httpContext.Features.Get<UmbracoRouteValues>();
            if (routeValues != null)
            {
                string culture = routeValues.PublishedRequest?.Culture;
                if (culture != null)
                {
                    lock (_locker)
                    {
                        // We need to dynamically change the supported cultures since we won't ever know what languages are used since
                        // they are dynamic within Umbraco.
                        // This code to check existence is borrowed from aspnetcore to avoid creating a CultureInfo
                        // https://github.com/dotnet/aspnetcore/blob/b795ac3546eb3e2f47a01a64feb3020794ca33bb/src/Middleware/Localization/src/RequestLocalizationMiddleware.cs#L165
                        CultureInfo existingCulture = _localizationOptions.SupportedCultures.FirstOrDefault(supportedCulture =>
                            StringSegment.Equals(supportedCulture.Name, culture, StringComparison.OrdinalIgnoreCase));

                        if (existingCulture == null)
                        {
                            // add this as a supporting culture
                            var ci = CultureInfo.GetCultureInfo(culture);
                            _localizationOptions.SupportedCultures.Add(ci);
                            _localizationOptions.SupportedUICultures.Add(ci);
                        }
                    }

                    return Task.FromResult(new ProviderCultureResult(culture));
                }
            }

            return NullProviderCultureResult;
        }

    }
}