Sets the negotiated interface language on the default configuration context.
\Symfony\Component\HttpKernel\Event\GetResponseEvent $event: Kernel event to respond to.
public function onKernelRequestSetDefaultConfigContextLocale(GetResponseEvent $event) {
// Re-initialize the default configuration context to ensure any cached
// configuration object are reset and can be translated. This will invoke
// the config context event which will retrieve the negotiated language
// from the language manager in configContext().
$this->defaultConfigContext
->init();
}