Language visibility condition on blocks does not work

Problem/Motivation

When a block is present on a page created by page manager, and this block is managed by regular Drupal block management, and it has language visibility condition, this condition does not apply correctly.

Steps to reproduce

You should have at least 2 languages on the site enabled, say, English and French. English is default.
Create a page manager page. It may be even empty. Let it have the path /test.
Put some block in some region by regular Drupal block management (admin/structure/blocks), and assign visibility condition Language -> English.
Put another block the same way at assign it visibility condition Language->French
Go to the /test page in English. You will see an English block. Switch to French. You will still see the English block.

Proposed resolution

The responsibility for this behaviour is somewhat shared between Core and Page manager.

\Drupal\language\Plugin\Condition\Language::evaluate() relies not on the language negotiator, but on the language context.

And here's the stack trace of how language context is set

Context.php:51, Drupal\Core\Plugin\Context\Context->__construct()
CurrentLanguageContext.php:55, Drupal\Core\Language\ContextProvider\CurrentLanguageContext->getRuntimeContexts()
CurrentLanguageContext.php:72, Drupal\Core\Language\ContextProvider\CurrentLanguageContext->getAvailableContexts()
LazyContextRepository.php:97, Drupal\Core\Plugin\Context\LazyContextRepository->getAvailableContexts()
EntityConverter.php:132, Drupal\Core\ParamConverter\EntityConverter->convert()
ParamConverterManager.php:100, Drupal\Core\ParamConverter\ParamConverterManager->convert()
ParamConversionEnhancer.php:45, Drupal\Core\Routing\Enhancer\ParamConversionEnhancer->enhance()
VariantRouteFilter.php:233, Drupal\page_manager\Routing\VariantRouteFilter->getRequestAttributes()
VariantRouteFilter.php:128, Drupal\page_manager\Routing\VariantRouteFilter->getVariantRouteName()
VariantRouteFilter.php:82, Drupal\page_manager\Routing\VariantRouteFilter->filter()
Router.php:280, Drupal\Core\Routing\Router->applyRouteFilters()
Router.php:126, Drupal\Core\Routing\Router->matchRequest()
AccessAwareRouter.php:93, Drupal\Core\Routing\AccessAwareRouter->matchRequest()
AccessAwareRouter.php:151, Drupal\Core\Routing\AccessAwareRouter->match()
LanguageNegotiationUserAdmin.php:138, Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUserAdmin->isAdminPath()
LanguageNegotiationUserAdmin.php:104, Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUserAdmin->getLangcode()
LanguageNegotiator.php:188, Drupal\language\LanguageNegotiator->negotiateLanguage()
LanguageNegotiator.php:133, Drupal\language\LanguageNegotiator->initializeType()
ConfigurableLanguageManager.php:218, Drupal\language\ConfigurableLanguageManager->getCurrentLanguage()
LanguageRequestSubscriber.php:92, Drupal\language\EventSubscriber\LanguageRequestSubscriber->setLanguageOverrides()
LanguageRequestSubscriber.php:74, Drupal\language\EventSubscriber\LanguageRequestSubscriber->onKernelRequestLanguage()
ContainerAwareEventDispatcher.php:142, call_user_func:{/var/www/html/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php:142}()
ContainerAwareEventDispatcher.php:142, Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch()
HttpKernel.php:134, Symfony\Component\HttpKernel\HttpKernel->handleRaw()
HttpKernel.php:80, Symfony\Component\HttpKernel\HttpKernel->handle()
Session.php:58, Drupal\Core\StackMiddleware\Session->handle()
KernelPreHandle.php:48, Drupal\Core\StackMiddleware\KernelPreHandle->handle()
PageCache.php:106, Drupal\page_cache\StackMiddleware\PageCache->pass()
PageCache.php:85, Drupal\page_cache\StackMiddleware\PageCache->handle()
ReverseProxyMiddleware.php:48, Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle()
NegotiationMiddleware.php:51, Drupal\Core\StackMiddleware\NegotiationMiddleware->handle()
StackedHttpKernel.php:23, Stack\StackedHttpKernel->handle()
DrupalKernel.php:708, Drupal\Core\DrupalKernel->handle()
index.php:19, {main}()

So router gets called from language negotiation, and this routing sets required contexts including language when language negotiation is not done yet.

I think \Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUserAdmin::isAdminPath() is wrong and should not build a route if there is no yet. Maybe there's also a way to approach this in Page Manager.

The solution that is quick and dirty is to use negotiated language in \Drupal\language\Plugin\Condition\Language::evaluate() , which means a core patch. I will cross-post this as a core issue and put the patch there.

Remaining tasks

Find a clean solution.

User interface changes

No.

API changes

?

Data model changes

?