7 files declare their use of LanguageNegotiatorInterface

ConfigSubscriber.php in core/modules/language/src/EventSubscriber/ConfigSubscriber.php
ConfigurableLanguageManagerSwitchLinksTest.php in core/modules/language/tests/src/Unit/ConfigurableLanguageManagerSwitchLinksTest.php
LanguageRequestSubscriber.php in core/modules/language/src/EventSubscriber/LanguageRequestSubscriber.php
LanguageUILanguageNegotiationTest.php in core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
NegotiationConfigureForm.php in core/modules/language/src/Form/NegotiationConfigureForm.php
PathProcessorLanguage.php in core/modules/language/src/HttpKernel/PathProcessorLanguage.php
PathProcessorTest.php in core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php

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