From fa1c3db5b26f9703cadfb9188932f530a2fd9dc1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Miklu=C5=A1ek?= <marek.miklusek@gmail.com>
Date: Fri, 24 Jul 2026 17:59:15 +0200
Subject: [PATCH 1/2] Fix multibyte case-insensitive matching in Str::replace
 and Str::remove

---
 src/Illuminate/Support/Str.php   | 47 ++++++++++++++++++++++++++++++--
 tests/Support/SupportStrTest.php |  8 ++++++
 2 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/src/Illuminate/Support/Str.php b/src/Illuminate/Support/Str.php
index 7cfa81d329e8..1b7da0f5e03b 100644
--- a/src/Illuminate/Support/Str.php
+++ b/src/Illuminate/Support/Str.php
@@ -1286,7 +1286,50 @@ public static function replace($search, $replace, $subject, $caseSensitive = tru
 
         return $caseSensitive
             ? str_replace($search, $replace, $subject)
-            : str_ireplace($search, $replace, $subject);
+            : static::replaceIgnoreCase($search, $replace, $subject);
+    }
+
+    /**
+     * Replace the given value in the given string regardless of case.
+     *
+     * @param  string|iterable<string>  $search
+     * @param  string|iterable<string>  $replace
+     * @param  string|iterable<string>  $subject
+     * @return string|string[]
+     */
+    protected static function replaceIgnoreCase($search, $replace, $subject)
+    {
+        $searches = is_array($search) ? array_values($search) : [$search];
+
+        if (static::isAscii(implode('', $searches))) {
+            return str_ireplace($search, $replace, $subject);
+        }
+
+        foreach ((array) $subject as $value) {
+            if (! preg_match('//u', (string) $value)) {
+                return str_ireplace($search, $replace, $subject);
+            }
+        }
+
+        $replacements = is_array($replace)
+            ? array_values($replace)
+            : array_fill(0, count($searches), $replace);
+
+        foreach ($searches as $index => $term) {
+            if ((string) $term === '') {
+                continue;
+            }
+
+            $replacement = (string) ($replacements[$index] ?? '');
+
+            $subject = preg_replace_callback(
+                '/'.preg_quote((string) $term, '/').'/iu',
+                fn () => $replacement,
+                $subject
+            );
+        }
+
+        return $subject;
     }
 
     /**
@@ -1419,7 +1462,7 @@ public static function remove($search, $subject, $caseSensitive = true)
 
         return $caseSensitive
             ? str_replace($search, '', $subject)
-            : str_ireplace($search, '', $subject);
+            : static::replaceIgnoreCase($search, '', $subject);
     }
 
     /**
diff --git a/tests/Support/SupportStrTest.php b/tests/Support/SupportStrTest.php
index b6a820b12078..2e9edc44607f 100755
--- a/tests/Support/SupportStrTest.php
+++ b/tests/Support/SupportStrTest.php
@@ -945,6 +945,11 @@ public function testReplace()
         $this->assertSame('foo/bar/baz', Str::replace(' ', '/', 'foo bar baz'));
         $this->assertSame('foo bar baz', Str::replace(['?1', '?2', '?3'], ['foo', 'bar', 'baz'], '?1 ?2 ?3'));
         $this->assertSame(['foo', 'bar', 'baz'], Str::replace(collect(['?1', '?2', '?3']), collect(['foo', 'bar', 'baz']), collect(['?1', '?2', '?3'])));
+
+        $this->assertSame('Xltý kôň', Str::replace('ž', 'X', 'Žltý kôň', false));
+        $this->assertSame('žltý pes', Str::replace('KÔŇ', 'pes', 'žltý kôň', false));
+        $this->assertSame('Xltý pes', Str::replace(['ž', 'KÔŇ'], ['X', 'pes'], 'Žltý kôň', false));
+        $this->assertSame(['Xltý', 'kôň'], Str::replace('ž', 'X', ['Žltý', 'kôň'], false));
     }
 
     public function testReplaceArray()
@@ -1026,6 +1031,9 @@ public function testRemove()
         $this->assertSame('Fooar', Str::remove(['f', 'b'], 'Foobar'));
         $this->assertSame('ooar', Str::remove(['f', 'b'], 'Foobar', false));
         $this->assertSame('Foobar', Str::remove(['f', '|'], 'Foo|bar'));
+
+        $this->assertSame('ltý', Str::remove('ž', 'Žltý', false));
+        $this->assertSame('žltý ', Str::remove('KÔŇ', 'žltý kôň', false));
     }
 
     public function testReverse()

From f7136ff8a0f43413e6ed979c10bad58c9e9e0ab1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Miklu=C5=A1ek?= <marek.miklusek@gmail.com>
Date: Fri, 24 Jul 2026 19:49:27 +0200
Subject: [PATCH 2/2] Fix docblock parameter types on replaceIgnoreCase

---
 src/Illuminate/Support/Str.php | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/Illuminate/Support/Str.php b/src/Illuminate/Support/Str.php
index 1b7da0f5e03b..388bab96b05f 100644
--- a/src/Illuminate/Support/Str.php
+++ b/src/Illuminate/Support/Str.php
@@ -1292,9 +1292,9 @@ public static function replace($search, $replace, $subject, $caseSensitive = tru
     /**
      * Replace the given value in the given string regardless of case.
      *
-     * @param  string|iterable<string>  $search
-     * @param  string|iterable<string>  $replace
-     * @param  string|iterable<string>  $subject
+     * @param  array|string  $search
+     * @param  array|string  $replace
+     * @param  array|string  $subject
      * @return string|string[]
      */
     protected static function replaceIgnoreCase($search, $replace, $subject)