17 files declare their use of LanguageNegotiationUrl

BlockUiTest.php in core/modules/block/tests/src/Functional/BlockUiTest.php
BookMultilingualTest.php in core/modules/book/tests/src/Kernel/BookMultilingualTest.php
EntityUrlLanguageTest.php in core/modules/language/tests/src/Kernel/EntityUrlLanguageTest.php
language.module in core/modules/language/language.module
Add language handling functionality to Drupal.
LanguageNegotiationContentEntityTest.php in core/modules/language/tests/src/Functional/LanguageNegotiationContentEntityTest.php
LanguageNegotiationUrlTest.php in core/modules/language/tests/src/Unit/LanguageNegotiationUrlTest.php
LanguageSwitchingTest.php in core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
LanguageUILanguageNegotiationTest.php in core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
LanguageUrlRewritingTest.php in core/modules/language/tests/src/Functional/LanguageUrlRewritingTest.php
LinksetControllerMultiLingualTest.php in core/modules/system/tests/src/Functional/Menu/LinksetControllerMultiLingualTest.php
MigrateLanguageNegotiationSettingsTest.php in core/modules/language/tests/src/Kernel/Migrate/d6/MigrateLanguageNegotiationSettingsTest.php
MigrateLanguageNegotiationSettingsTest.php in core/modules/language/tests/src/Kernel/Migrate/d7/MigrateLanguageNegotiationSettingsTest.php
NegotiationUrlForm.php in core/modules/language/src/Form/NegotiationUrlForm.php
NodeFieldMultilingualTest.php in core/modules/node/tests/src/Functional/NodeFieldMultilingualTest.php
PageCacheTagsIntegrationTest.php in core/modules/page_cache/tests/src/Functional/PageCacheTagsIntegrationTest.php
PathLanguageTest.php in core/modules/path/tests/src/Functional/PathLanguageTest.php
PathProcessorTest.php in core/tests/Drupal/Tests/Core/PathProcessor/PathProcessorTest.php

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