app/Http/Kernel.php

@@ -63,5 +63,6 @@ class Kernel extends HttpKernel
         'signed' => \App\Http\Middleware\ValidateSignature::class,
         'throttle' => \Illuminate\Routing\Middleware\ThrottleRequestsWithRedis::class,
         'verified' => \App\Http\Middleware\EnsureUserIsVerified::class,
+        'user.locale' => \App\Http\Middleware\UserLocale::class,
     ];
 }

app/Http/Middleware/UserLocale.php

@@ -0,0 +1,19 @@
+<?php declare(strict_types=1);
+
+namespace App\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\App;
+
+final class UserLocale
+{
+    public function handle(Request $request, Closure $next)
+    {
+        if ($request->user() && $request->user()->lang) {
+            App::setLocale($request->user()->lang->getLocale());
+        }
+
+        return $next($request);
+    }
+}