diff --git a/src/Symfony/Component/HttpFoundation/Request.php b/src/Symfony/Component/HttpFoundation/Request.php
index 2c3d824694eb..df332479de20 100644
--- a/src/Symfony/Component/HttpFoundation/Request.php
+++ b/src/Symfony/Component/HttpFoundation/Request.php
@@ -1532,24 +1532,25 @@ public function getPreferredLanguage(?array $locales = null): ?string
             return $preferredLanguages[0] ?? null;
         }
 
+        $locales = array_map($this->formatLocale(...), $locales ?? []);
         if (!$preferredLanguages) {
             return $locales[0];
         }
 
-        $extendedPreferredLanguages = [];
-        foreach ($preferredLanguages as $language) {
-            $extendedPreferredLanguages[] = $language;
-            if (false !== $position = strpos($language, '_')) {
-                $superLanguage = substr($language, 0, $position);
-                if (!\in_array($superLanguage, $preferredLanguages, true)) {
-                    $extendedPreferredLanguages[] = $superLanguage;
+        if ($matches = array_intersect($preferredLanguages, $locales)) {
+            return current($matches);
+        }
+
+        $combinations = array_merge(...array_map($this->getLanguageCombinations(...), $preferredLanguages));
+        foreach ($combinations as $combination) {
+            foreach ($locales as $locale) {
+                if (str_starts_with($locale, $combination)) {
+                    return $locale;
                 }
             }
         }
 
-        $preferredLanguages = array_values(array_intersect($extendedPreferredLanguages, $locales));
-
-        return $preferredLanguages[0] ?? $locales[0];
+        return $locales[0];
     }
 
     /**
@@ -1567,32 +1568,91 @@ public function getLanguages(): array
         $this->languages = [];
         foreach ($languages as $acceptHeaderItem) {
             $lang = $acceptHeaderItem->getValue();
-            if (str_contains($lang, '-')) {
-                $codes = explode('-', $lang);
-                if ('i' === $codes[0]) {
-                    // Language not listed in ISO 639 that are not variants
-                    // of any listed language, which can be registered with the
-                    // i-prefix, such as i-cherokee
-                    if (\count($codes) > 1) {
-                        $lang = $codes[1];
-                    }
-                } else {
-                    for ($i = 0, $max = \count($codes); $i < $max; ++$i) {
-                        if (0 === $i) {
-                            $lang = strtolower($codes[0]);
-                        } else {
-                            $lang .= '_'.strtoupper($codes[$i]);
-                        }
-                    }
-                }
-            }
-
-            $this->languages[] = $lang;
+            $this->languages[] = $this->formatLocale($lang);
         }
+        $this->languages = array_unique($this->languages);
 
         return $this->languages;
     }
 
+    /**
+     * Strips the locale to only keep the canonicalized language value.
+     *
+     * Depending on the $locale value, this method can return values like :
+     * - language_Script_REGION: "fr_Latn_FR", "zh_Hans_TW"
+     * - language_Script: "fr_Latn", "zh_Hans"
+     * - language_REGION: "fr_FR", "zh_TW"
+     * - language: "fr", "zh"
+     *
+     * Invalid locale values are returned as is.
+     *
+     * @see https://wikipedia.org/wiki/IETF_language_tag
+     * @see https://datatracker.ietf.org/doc/html/rfc5646
+     */
+    private static function formatLocale(string $locale): string
+    {
+        [$language, $script, $region] = self::getLanguageComponents($locale);
+
+        return implode('_', array_filter([$language, $script, $region]));
+    }
+
+    /**
+     * Returns an array of all possible combinations of the language components.
+     *
+     * For instance, if the locale is "fr_Latn_FR", this method will return:
+     * - "fr_Latn_FR"
+     * - "fr_Latn"
+     * - "fr_FR"
+     * - "fr"
+     *
+     * @return string[]
+     */
+    private static function getLanguageCombinations(string $locale): array
+    {
+        [$language, $script, $region] = self::getLanguageComponents($locale);
+
+        return array_unique([
+            implode('_', array_filter([$language, $script, $region])),
+            implode('_', array_filter([$language, $script])),
+            implode('_', array_filter([$language, $region])),
+            $language,
+        ]);
+    }
+
+    /**
+     * Returns an array with the language components of the locale.
+     *
+     * For example:
+     * - If the locale is "fr_Latn_FR", this method will return "fr", "Latn", "FR"
+     * - If the locale is "fr_FR", this method will return "fr", null, "FR"
+     * - If the locale is "zh_Hans", this method will return "zh", "Hans", null
+     *
+     * @see https://wikipedia.org/wiki/IETF_language_tag
+     * @see https://datatracker.ietf.org/doc/html/rfc5646
+     *
+     * @return array{string, string|null, string|null}
+     */
+    private static function getLanguageComponents(string $locale): array
+    {
+        $locale = str_replace('_', '-', strtolower($locale));
+        $pattern = '/^([a-zA-Z]{2,3}|i-[a-zA-Z]{5,})(?:-([a-zA-Z]{4}))?(?:-([a-zA-Z]{2}))?(?:-(.+))?$/';
+        if (!preg_match($pattern, $locale, $matches)) {
+            return [$locale, null, null];
+        }
+        if (str_starts_with($matches[1], 'i-')) {
+            // Language not listed in ISO 639 that are not variants
+            // of any listed language, which can be registered with the
+            // i-prefix, such as i-cherokee
+            $matches[1] = substr($matches[1], 2);
+        }
+
+        return [
+            $matches[1],
+            isset($matches[2]) ? ucfirst(strtolower($matches[2])) : null,
+            isset($matches[3]) ? strtoupper($matches[3]) : null,
+        ];
+    }
+
     /**
      * Gets a list of charsets acceptable by the client browser in preferable order.
      *
diff --git a/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php b/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
index 68cb6ee43bed..89b38ae92b79 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
@@ -1502,27 +1502,43 @@ public function testGetPreferredLanguage()
     {
         $request = new Request();
         $this->assertNull($request->getPreferredLanguage());
-        $this->assertNull($request->getPreferredLanguage([]));
-        $this->assertEquals('fr', $request->getPreferredLanguage(['fr']));
-        $this->assertEquals('fr', $request->getPreferredLanguage(['fr', 'en']));
-        $this->assertEquals('en', $request->getPreferredLanguage(['en', 'fr']));
-        $this->assertEquals('fr-ch', $request->getPreferredLanguage(['fr-ch', 'fr-fr']));
-
-        $request = new Request();
-        $request->headers->set('Accept-language', 'zh, en-us; q=0.8, en; q=0.6');
-        $this->assertEquals('en', $request->getPreferredLanguage(['en', 'en-us']));
-
-        $request = new Request();
-        $request->headers->set('Accept-language', 'zh, en-us; q=0.8, en; q=0.6');
-        $this->assertEquals('en', $request->getPreferredLanguage(['fr', 'en']));
-
-        $request = new Request();
-        $request->headers->set('Accept-language', 'zh, en-us; q=0.8');
-        $this->assertEquals('en', $request->getPreferredLanguage(['fr', 'en']));
+    }
 
+    /**
+     * @dataProvider providePreferredLanguage
+     */
+    public function testPreferredLanguageWithLocales(?string $expectedLocale, ?string $acceptLanguage, array $locales)
+    {
         $request = new Request();
-        $request->headers->set('Accept-language', 'zh, en-us; q=0.8, fr-fr; q=0.6, fr; q=0.5');
-        $this->assertEquals('en', $request->getPreferredLanguage(['fr', 'en']));
+        if ($acceptLanguage) {
+            $request->headers->set('Accept-language', $acceptLanguage);
+        }
+        $this->assertSame($expectedLocale, $request->getPreferredLanguage($locales));
+    }
+
+    public static function providePreferredLanguage(): iterable
+    {
+        yield '"es_PA" is selected as no supported locale is set' => ['es_PA', 'es-pa, en-us; q=0.8, en; q=0.6', []];
+        yield 'No supported locales' => [null, null, []];
+        yield '"fr" selected as first choice when no header is present' => ['fr', null, ['fr', 'en']];
+        yield '"en" selected as first choice when no header is present' => ['en', null, ['en', 'fr']];
+        yield '"fr_CH" selected as first choice when no header is present' => ['fr_CH', null, ['fr-ch', 'fr-fr']];
+        yield '"en_US" is selected as an exact match is found (1)' => ['en_US', 'zh, en-us; q=0.8, en; q=0.6', ['en', 'en-us']];
+        yield '"en_US" is selected as an exact match is found (2)' => ['en_US', 'ja-JP,fr_CA;q=0.7,fr;q=0.5,en_US;q=0.3', ['en_US', 'fr_FR']];
+        yield '"en" is selected as an exact match is found' => ['en', 'zh, en-us; q=0.8, en; q=0.6', ['fr', 'en']];
+        yield '"fr" is selected as an exact match is found' => ['fr', 'zh, en-us; q=0.8, fr-fr; q=0.6, fr; q=0.5', ['fr', 'en']];
+        yield '"en" is selected as "en-us" is a similar dialect' => ['en', 'zh, en-us; q=0.8', ['fr', 'en']];
+        yield '"fr_FR" is selected as "fr_CA" is a similar dialect (1)' => ['fr_FR', 'ja-JP,fr_CA;q=0.7,fr;q=0.5', ['en_US', 'fr_FR']];
+        yield '"fr_FR" is selected as "fr_CA" is a similar dialect (2)' => ['fr_FR', 'ja-JP,fr_CA;q=0.7', ['en_US', 'fr_FR']];
+        yield '"fr_FR" is selected as "fr" is a similar dialect' => ['fr_FR', 'ja-JP,fr;q=0.5', ['en_US', 'fr_FR']];
+        yield '"fr_FR" is selected as "fr_CA" is a similar dialect and has a greater "q" compared to "en_US" (2)' => ['fr_FR', 'ja-JP,fr_CA;q=0.7,ru-ru;q=0.3', ['en_US', 'fr_FR']];
+        yield '"en_US" is selected it is an exact match' => ['en_US', 'ja-JP,fr;q=0.5,en_US;q=0.3', ['en_US', 'fr_FR']];
+        yield '"fr_FR" is selected as "fr_CA" is a similar dialect and has a greater "q" compared to "en"' => ['fr_FR', 'ja-JP,fr_CA;q=0.7,en;q=0.5', ['en_US', 'fr_FR']];
+        yield '"fr_FR" is selected as is is an exact match as well as "en_US", but with a greater "q" parameter' => ['fr_FR', 'en-us;q=0.5,fr-fr', ['en_US', 'fr_FR']];
+        yield '"hi_IN" is selected as "hi_Latn_IN" is a similar dialect' => ['hi_IN', 'fr-fr,hi_Latn_IN;q=0.5', ['hi_IN', 'en_US']];
+        yield '"hi_Latn_IN" is selected as "hi_IN" is a similar dialect' => ['hi_Latn_IN', 'fr-fr,hi_IN;q=0.5', ['hi_Latn_IN', 'en_US']];
+        yield '"en_US" is selected as "en_Latn_US+variants+extensions" is a similar dialect' => ['en_US', 'en-latn-us-fonapi-u-nu-numerical-x-private,fr;q=0.5', ['fr_FR', 'en_US']];
+        yield '"zh_Hans" is selected over "zh_TW" as the script as a greater priority over the region' => ['zh_Hans', 'zh-hans-tw, zh-hant-tw', ['zh_Hans', 'zh_tw']];
     }
 
     public function testIsXmlHttpRequest()
@@ -1601,30 +1617,28 @@ public function testGetAcceptableContentTypes()
         $this->assertEquals(['application/vnd.wap.wmlscriptc', 'text/vnd.wap.wml', 'application/vnd.wap.xhtml+xml', 'application/xhtml+xml', 'text/html', 'multipart/mixed', '*/*'], $request->getAcceptableContentTypes());
     }
 
-    public function testGetLanguages()
+    /**
+     * @dataProvider provideLanguages
+     */
+    public function testGetLanguages(array $expectedLocales, ?string $acceptLanguage)
     {
         $request = new Request();
-        $this->assertEquals([], $request->getLanguages());
-
-        $request = new Request();
-        $request->headers->set('Accept-language', 'zh, en-us; q=0.8, en; q=0.6');
-        $this->assertEquals(['zh', 'en_US', 'en'], $request->getLanguages());
-
-        $request = new Request();
-        $request->headers->set('Accept-language', 'zh, en-us; q=0.6, en; q=0.8');
-        $this->assertEquals(['zh', 'en', 'en_US'], $request->getLanguages()); // Test out of order qvalues
-
-        $request = new Request();
-        $request->headers->set('Accept-language', 'zh, en, en-us');
-        $this->assertEquals(['zh', 'en', 'en_US'], $request->getLanguages()); // Test equal weighting without qvalues
-
-        $request = new Request();
-        $request->headers->set('Accept-language', 'zh; q=0.6, en, en-us; q=0.6');
-        $this->assertEquals(['en', 'zh', 'en_US'], $request->getLanguages()); // Test equal weighting with qvalues
+        if ($acceptLanguage) {
+            $request->headers->set('Accept-language', $acceptLanguage);
+        }
+        $this->assertEquals($expectedLocales, $request->getLanguages());
+    }
 
-        $request = new Request();
-        $request->headers->set('Accept-language', 'zh, i-cherokee; q=0.6');
-        $this->assertEquals(['zh', 'cherokee'], $request->getLanguages());
+    public static function provideLanguages(): iterable
+    {
+        yield 'empty' => [[], null];
+        yield [['zh', 'en_US', 'en'], 'zh, en-us; q=0.8, en; q=0.6'];
+        yield 'Test out of order qvalues' => [['zh', 'en', 'en_US'], 'zh, en-us; q=0.6, en; q=0.8'];
+        yield 'Test equal weighting without qvalues' => [['zh', 'en', 'en_US'], 'zh, en, en-us'];
+        yield 'Test equal weighting with qvalues' => [['en', 'zh', 'en_US'], 'zh; q=0.6, en, en-us; q=0.6'];
+        yield 'Test irregular locale' => [['zh', 'cherokee'], 'zh, i-cherokee; q=0.6'];
+        yield 'Test with variants, unicode extensions and private information' => [['pt_BR', 'hy_Latn_IT', 'zh_Hans_TW'], 'pt-BR-u-ca-gregory-nu-latn, hy-Latn-IT-arevela, zh-Hans-TW-fonapi-u-islamcal-x-AZE-derbend; q=0.6'];
+        yield 'Test multiple regions' => [['en_US', 'en_CA', 'en_GB', 'en'], 'en-us, en-ca, en-gb, en'];
     }
 
     public function testGetAcceptHeadersReturnString()
@@ -2199,7 +2213,7 @@ public function testFactory()
 
     public function testFactoryCallable()
     {
-        $requestFactory = new class {
+        $requestFactory = new class() {
             public function createRequest(): Request
             {
                 return new NewRequest();
@@ -2211,7 +2225,6 @@ public function createRequest(): Request
         $this->assertEquals('foo', Request::create('/')->getFoo());
 
         Request::setFactory(null);
-
     }
 
     /**