diff --git a/ChangeLog-12.0.md b/ChangeLog-12.0.md
index 0023d08bd10..74aa5c5af7c 100644
--- a/ChangeLog-12.0.md
+++ b/ChangeLog-12.0.md
@@ -7,6 +7,7 @@ All notable changes of the PHPUnit 12.0 release series are documented in this fi
 ### Removed
 
 * [#5215](https://github.com/sebastianbergmann/phpunit/issues/5215): `TestCase::iniSet()`
+* [#5217](https://github.com/sebastianbergmann/phpunit/issues/5217): `TestCase::setLocale()`
 * [#5246](https://github.com/sebastianbergmann/phpunit/issues/5246): `TestCase::createTestProxy()`
 * [#5247](https://github.com/sebastianbergmann/phpunit/issues/5247): `TestCase::getMockForAbstractClass()`
 * [#5248](https://github.com/sebastianbergmann/phpunit/issues/5248): `TestCase::getMockFromWsdl()`
diff --git a/DEPRECATIONS.md b/DEPRECATIONS.md
index 6d93b95eac0..e0ce95cbc48 100644
--- a/DEPRECATIONS.md
+++ b/DEPRECATIONS.md
@@ -47,7 +47,6 @@ This functionality is currently [hard-deprecated](https://phpunit.de/backward-co
 | Issue                                                             | Description                                                 | Since  | Replacement                                                                             |
 |-------------------------------------------------------------------|-------------------------------------------------------------|--------|-----------------------------------------------------------------------------------------|
 | [#4505](https://github.com/sebastianbergmann/phpunit/issues/4505) | Metadata in doc-comments                                    | 10.3.0 | Metadata in attributes                                                                  |
-| [#5216](https://github.com/sebastianbergmann/phpunit/issues/5216) | `TestCase::setLocale()`                                     | 10.3.0 |                                                                                         |
 | [#5800](https://github.com/sebastianbergmann/phpunit/issues/5800) | Targeting traits with `#[CoversClass]` and `#[UsesClass]`   | 11.2.0 | `#[CoversClass]` and `#[UsesClass]` also target the traits used by the targeted classes |
 | [#5951](https://github.com/sebastianbergmann/phpunit/issues/5951) | `includeUncoveredFiles` configuration option                | 11.4.0 |                                                                                         |
 | [#5958](https://github.com/sebastianbergmann/phpunit/issues/5958) | `#[CoversTrait]` and `#[UsesTrait]` attributes              | 11.4.0 | `#[CoversClass]` and `#[UsesClass]` also target the traits used by the targeted classes |
diff --git a/src/Framework/TestCase.php b/src/Framework/TestCase.php
index 65e58f5e17d..793dd04abd2 100644
--- a/src/Framework/TestCase.php
+++ b/src/Framework/TestCase.php
@@ -9,12 +9,6 @@
  */
 namespace PHPUnit\Framework;
 
-use const LC_ALL;
-use const LC_COLLATE;
-use const LC_CTYPE;
-use const LC_MONETARY;
-use const LC_NUMERIC;
-use const LC_TIME;
 use const PHP_EOL;
 use function array_keys;
 use function array_merge;
@@ -48,7 +42,6 @@
 use function restore_exception_handler;
 use function set_error_handler;
 use function set_exception_handler;
-use function setlocale;
 use function sprintf;
 use function str_contains;
 use function trim;
@@ -111,8 +104,7 @@
  */
 abstract class TestCase extends Assert implements Reorderable, SelfDescribing, Test
 {
-    private const LOCALE_CATEGORIES = [LC_ALL, LC_COLLATE, LC_CTYPE, LC_MONETARY, LC_NUMERIC, LC_TIME];
-    private ?bool $backupGlobals    = null;
+    private ?bool $backupGlobals = null;
 
     /**
      * @var list<string>
@@ -175,11 +167,6 @@ abstract class TestCase extends Assert implements Reorderable, SelfDescribing, T
      */
     private array $dependencyInput = [];
 
-    /**
-     * @var array<int, non-empty-string>
-     */
-    private array $locale = [];
-
     /**
      * @var list<MockObjectInternal>
      */
@@ -639,7 +626,6 @@ final public function runBare(): void
         $this->restoreGlobalErrorExceptionHandlers();
         $this->restoreGlobalState();
         $this->unregisterCustomComparators();
-        $this->cleanupLocaleSettings();
         libxml_clear_errors();
 
         $this->testValueObjectForEvents = null;
@@ -1234,50 +1220,6 @@ final protected function runTest(): mixed
         return $testResult;
     }
 
-    /**
-     * This method is a wrapper for the setlocale() function that automatically
-     * resets the locale to its original value after the test is run.
-     *
-     * @throws Exception
-     *
-     * @deprecated https://github.com/sebastianbergmann/phpunit/issues/5216
-     *
-     * @codeCoverageIgnore
-     */
-    final protected function setLocale(mixed ...$arguments): void
-    {
-        Event\Facade::emitter()->testTriggeredPhpunitDeprecation(
-            $this->valueObjectForEvents(),
-            'setLocale() is deprecated and will be removed in PHPUnit 12 without replacement.',
-        );
-
-        if (count($arguments) < 2) {
-            throw new Exception;
-        }
-
-        [$category, $locale] = $arguments;
-
-        if (!in_array($category, self::LOCALE_CATEGORIES, true)) {
-            throw new Exception;
-        }
-
-        if (!is_array($locale) && !is_string($locale)) {
-            throw new Exception;
-        }
-
-        $this->locale[$category] = setlocale($category, '0');
-
-        $result = setlocale(...$arguments);
-
-        if ($result === false) {
-            throw new Exception(
-                'The locale functionality is not implemented on your platform, ' .
-                'the specified locale does not exist or the category name is ' .
-                'invalid.',
-            );
-        }
-    }
-
     /**
      * Creates a mock object for the specified interface or class.
      *
@@ -1919,15 +1861,6 @@ private function unregisterCustomComparators(): void
         $this->customComparators = [];
     }
 
-    private function cleanupLocaleSettings(): void
-    {
-        foreach ($this->locale as $category => $locale) {
-            setlocale($category, $locale);
-        }
-
-        $this->locale = [];
-    }
-
     /**
      * @throws Exception
      */