Use get methods to access application locale (#44521)

* Fix access config translation service provider

* Fix access config translation service provider

Author: Antoine B

src/Illuminate/Translation/TranslationServiceProvider.php

@@ -22,11 +22,11 @@ public function register()
             // When registering the translator component, we'll need to set the default
             // locale as well as the fallback locale. So, we'll grab the application
             // configuration so we can easily get both of these values from there.
-            $locale = $app['config']['app.locale'];
+            $locale = $app->getLocale();
 
             $trans = new Translator($loader, $locale);
 
-            $trans->setFallback($app['config']['app.fallback_locale']);
+            $trans->setFallback($app->getFallbackLocale());
 
             return $trans;
         });