Add Accept-Language header support for per-request localization

Emby.Server.Implementations/HttpServer/WebSocketManager.cs

@@ -4,9 +4,11 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
 using System.Net.WebSockets;
 using System.Threading.Tasks;
+using Emby.Server.Implementations.Localization;
 using MediaBrowser.Common.Extensions;
 using MediaBrowser.Controller.Net;
 using Microsoft.AspNetCore.Http;
@@ -48,13 +50,22 @@ namespace Emby.Server.Implementations.HttpServer
 
                 WebSocket webSocket = await context.WebSockets.AcceptWebSocketAsync().ConfigureAwait(false);
 
+                // Capture the culture context set by AcceptLanguageMiddleware so it can be
+                // restored both when processing incoming messages and when periodic
+                // listeners produce server-initiated payloads on background tasks.
                 var connection = new WebSocketConnection(
                     _loggerFactory.CreateLogger<WebSocketConnection>(),
                     webSocket,
                     authorizationInfo,
                     context.GetNormalizedRemoteIP())
                 {
-                    OnReceive = ProcessWebSocketMessageReceived
+                    RequestCultureFallback = LocalizationManager.RequestCultureFallback,
+                    RequestUICulture = CultureInfo.CurrentUICulture.Name
+                };
+                connection.OnReceive = result =>
+                {
+                    connection.ApplyRequestCulture();
+                    return ProcessWebSocketMessageReceived(result);
                 };
                 await using (connection.ConfigureAwait(false))
                 {