9 files declare their use of LanguageDefault in Drupal 8

ActiveLinkResponseFilterTest.php in core/tests/Drupal/Tests/Core/EventSubscriber/ActiveLinkResponseFilterTest.php

ConfigSubscriber.php in core/modules/language/src/EventSubscriber/ConfigSubscriber.php

ConfigurableLanguageManager.php in core/modules/language/src/ConfigurableLanguageManager.php

ContextDefinitionIsSatisfiedTest.php in core/tests/Drupal/Tests/Core/Plugin/Context/ContextDefinitionIsSatisfiedTest.php

EntityContextDefinitionIsSatisfiedTest.php in core/tests/Drupal/Tests/Core/Plugin/Context/EntityContextDefinitionIsSatisfiedTest.php

HelpTopicSection.php in core/modules/help_topics/src/Plugin/HelpSection/HelpTopicSection.php

LanguageConfigFactoryOverride.php in core/modules/language/src/Config/LanguageConfigFactoryOverride.php

LanguageConfigFactoryOverrideInterface.php in core/modules/language/src/Config/LanguageConfigFactoryOverrideInterface.php

TranslationManager.php in core/lib/Drupal/Core/StringTranslation/TranslationManager.php