diff --git a/core/lib/Drupal/Core/Mail/MailFormatHelper.php b/core/lib/Drupal/Core/Mail/MailFormatHelper.php
index 2d8fe99a8a3beef3e070c7b31150ef24bfaaa31a..c17da77f7bfcc981515a560dee5cbc9a206f6748 100644
--- a/core/lib/Drupal/Core/Mail/MailFormatHelper.php
+++ b/core/lib/Drupal/Core/Mail/MailFormatHelper.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Utility\Html;
 use Drupal\Component\Utility\String;
+use Drupal\Component\Utility\Unicode;
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Site\Settings;
 
@@ -264,7 +265,7 @@ public static function htmlToText($string, $allowed_tags = NULL) {
         // Convert inline HTML text to plain text; not removing line-breaks or
         // white-space, since that breaks newlines when sanitizing plain-text.
         $value = trim(String::decodeEntities($value));
-        if (drupal_strlen($value)) {
+        if (Unicode::strlen($value)) {
           $chunk = $value;
         }
       }
diff --git a/core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php b/core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php
index 54f36484504edeb21325d5bb182702c53cbf5728..cdb724686b387a6dec0394d95ca17e7eeed6e4eb 100644
--- a/core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php
+++ b/core/lib/Drupal/Core/TypedData/Plugin/DataType/ItemList.php
@@ -99,7 +99,7 @@ public function getString() {
         $strings[] = $item->getString();
       }
       // Remove any empty strings resulting from empty items.
-      return implode(', ', array_filter($strings, 'drupal_strlen'));
+      return implode(', ', array_filter($strings, '\Drupal\Component\Utility\Unicode::strlen'));
     }
   }
 
diff --git a/core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php b/core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php
index bc699ccb75f9e604e71cda1ef5e8232350f7bd21..abb1c9c39b89d1a441502106af1eef2dd931c682 100644
--- a/core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php
+++ b/core/lib/Drupal/Core/TypedData/Plugin/DataType/Map.php
@@ -115,7 +115,7 @@ public function getString() {
       $strings[] = $property->getString();
     }
     // Remove any empty strings resulting from empty items.
-    return implode(', ', array_filter($strings, 'drupal_strlen'));
+    return implode(', ', array_filter($strings, '\Drupal\Component\Utility\Unicode::strlen'));
   }
 
   /**
diff --git a/core/modules/filter/filter.module b/core/modules/filter/filter.module
index 7af67322e9e4d25451eb81f11a8a83e65716e55c..a14d730ac80ad48e5f9437b923248af56661bb19 100644
--- a/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -784,7 +784,7 @@ function _filter_html_escape($text) {
 function _filter_html_image_secure_process($text) {
   // Find the path (e.g. '/') to Drupal root.
   $base_path = base_path();
-  $base_path_length = drupal_strlen($base_path);
+  $base_path_length = Unicode::strlen($base_path);
 
   // Find the directory on the server where index.php resides.
   $local_dir = DRUPAL_ROOT . '/';
diff --git a/core/modules/image/image.field.inc b/core/modules/image/image.field.inc
index 4668e2600e39539c08280afefede12ca264a4f9c..3f44993c46fa3e82f7e8a59276c2d5ba58d7bb58 100644
--- a/core/modules/image/image.field.inc
+++ b/core/modules/image/image.field.inc
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Render\Element;
 
 /**
@@ -64,7 +65,7 @@ function template_preprocess_image_formatter(&$variables) {
   $item = $variables['item'];
 
   // Do not output an empty 'title' attribute.
-  if (drupal_strlen($item->title) != 0) {
+  if (Unicode::strlen($item->title) != 0) {
     $variables['image']['#title'] = $item->title;
   }
 
diff --git a/core/modules/menu_ui/src/Tests/MenuTest.php b/core/modules/menu_ui/src/Tests/MenuTest.php
index c35d0d1caddba01931e74fc9a17fd7967dc58f91..1b09615e08c719057caaaf43ebb99984a1ccbac7 100644
--- a/core/modules/menu_ui/src/Tests/MenuTest.php
+++ b/core/modules/menu_ui/src/Tests/MenuTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\menu_ui\Tests;
 
 use Drupal\Component\Serialization\Json;
+use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Menu\MenuLinkInterface;
 use Drupal\menu_link_content\Entity\MenuLinkContent;
 use Drupal\system\Entity\Menu;
@@ -175,7 +176,7 @@ function addCustomMenu() {
     $this->assertRaw(t('!name cannot be longer than %max characters but is currently %length characters long.', array(
       '!name' => t('Menu name'),
       '%max' => MENU_MAX_MENU_NAME_LENGTH_UI,
-      '%length' => drupal_strlen($menu_name),
+      '%length' => Unicode::strlen($menu_name),
     )));
 
     // Change the menu_name so it no longer exceeds the maximum length.
@@ -187,7 +188,7 @@ function addCustomMenu() {
     $this->assertNoRaw(t('!name cannot be longer than %max characters but is currently %length characters long.', array(
       '!name' => t('Menu name'),
       '%max' => MENU_MAX_MENU_NAME_LENGTH_UI,
-      '%length' => drupal_strlen($menu_name),
+      '%length' => Unicode::strlen($menu_name),
     )));
     // Verify that the confirmation message is displayed.
     $this->assertRaw(t('Menu %label has been added.', array('%label' => $label)));
diff --git a/core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php b/core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php
index 37053c3434b9317934d6225e401e5b2d3b5c2a6b..d74049a54ea28c2054ccc8b35e366cbcd20ad1f0 100644
--- a/core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php
+++ b/core/modules/options/src/Plugin/Field/FieldType/ListStringItem.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\options\Plugin\Field\FieldType;
 
+use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Field\FieldStorageDefinitionInterface;
 use Drupal\Core\TypedData\DataDefinition;
 
@@ -68,7 +69,7 @@ protected function allowedValuesDescription() {
    * {@inheritdoc}
    */
   protected static function validateAllowedValue($option) {
-    if (drupal_strlen($option) > 255) {
+    if (Unicode::strlen($option) > 255) {
       return t('Allowed values list: each key must be a string at most 255 characters long.');
     }
   }
diff --git a/core/modules/responsive_image/responsive_image.module b/core/modules/responsive_image/responsive_image.module
index 79928157af1ef42c507ec85820fa7f2a1b171b02..bdb2a8320716994d3d4321846ac6dd30444006a3 100644
--- a/core/modules/responsive_image/responsive_image.module
+++ b/core/modules/responsive_image/responsive_image.module
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Routing\RouteMatchInterface;
 use \Drupal\Core\Template\Attribute;
 use Drupal\Core\Url;
@@ -144,7 +145,7 @@ function theme_responsive_image_formatter($variables) {
     $responsive_image['#entity'] = $entity;
   }
   $responsive_image['#alt'] = $item->alt;
-  if (drupal_strlen($item->title) != 0) {
+  if (Unicode::strlen($item->title) != 0) {
     $responsive_image['#title'] = $item->title;
   }
   // @todo Add support for route names.
diff --git a/core/modules/search/search.module b/core/modules/search/search.module
index e780087b0618422f60093fcd347ed1b81c69ec10..1ebe99d153ff7c55635f8212a9ba7819c2a1398e 100644
--- a/core/modules/search/search.module
+++ b/core/modules/search/search.module
@@ -306,7 +306,7 @@ function search_simplify($text, $langcode = NULL) {
 function search_expand_cjk($matches) {
   $min = \Drupal::config('search.settings')->get('index.minimum_word_size');
   $str = $matches[0];
-  $length = drupal_strlen($str);
+  $length = Unicode::strlen($str);
   // If the text is shorter than the minimum word size, don't tokenize it.
   if ($length <= $min) {
     return ' ' . $str . ' ';
@@ -453,7 +453,7 @@ function search_index($sid, $type, $text, $langcode) {
           // Add word to accumulator
           $accum .= $word . ' ';
           // Check wordlength
-          if (is_numeric($word) || drupal_strlen($word) >= $minimum_word_size) {
+          if (is_numeric($word) || Unicode::strlen($word) >= $minimum_word_size) {
             if (!isset($scored_words[$word])) {
               $scored_words[$word] = 0;
             }
diff --git a/core/modules/search/src/SearchQuery.php b/core/modules/search/src/SearchQuery.php
index b3e2cac5eab07b597b6324f7d597039ace91549d..21c271bfc50c488b64b553dbd6641926b5e61242 100644
--- a/core/modules/search/src/SearchQuery.php
+++ b/core/modules/search/src/SearchQuery.php
@@ -9,6 +9,7 @@
 
 namespace Drupal\search;
 
+use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Database\Query\SelectExtender;
 use Drupal\Core\Database\StatementEmpty;
 
@@ -367,7 +368,7 @@ protected function parseWord($word) {
     $split = explode(' ', $word);
     foreach ($split as $s) {
       $num = is_numeric($s);
-      if ($num || drupal_strlen($s) >= \Drupal::config('search.settings')->get('index.minimum_word_size')) {
+      if ($num || Unicode::strlen($s) >= \Drupal::config('search.settings')->get('index.minimum_word_size')) {
         if (!isset($this->words[$s])) {
           $this->words[$s] = $s;
           $num_new_scores++;
diff --git a/core/modules/search/src/Tests/SearchSimplifyTest.php b/core/modules/search/src/Tests/SearchSimplifyTest.php
index 848f7b7e84853bd7ba8adf6adc0d2b014e450c1d..d1c2774233dfa7878662a2fdb7db5dbcf188ac47 100644
--- a/core/modules/search/src/Tests/SearchSimplifyTest.php
+++ b/core/modules/search/src/Tests/SearchSimplifyTest.php
@@ -39,7 +39,7 @@ function testSearchSimplifyUnicode() {
         // Split this into 30-character chunks, so we don't run into limits
         // of truncation in search_simplify().
         $start = 0;
-        while ($start < drupal_strlen($string)) {
+        while ($start < Unicode::strlen($string)) {
           $newstr = Unicode::substr($string, $start, 30);
           // Special case: leading zeros are removed from numeric strings,
           // and there's one string in this file that is numbers starting with
@@ -54,7 +54,7 @@ function testSearchSimplifyUnicode() {
     }
     foreach ($strings as $key => $string) {
       $simplified = search_simplify($string);
-      $this->assertTrue(drupal_strlen($simplified) >= drupal_strlen($string), "Nothing is removed from string $key.");
+      $this->assertTrue(Unicode::strlen($simplified) >= Unicode::strlen($string), "Nothing is removed from string $key.");
     }
 
     // Test the low-numbered ASCII control characters separately. They are not
diff --git a/core/modules/system/src/Tests/Mail/HtmlToTextTest.php b/core/modules/system/src/Tests/Mail/HtmlToTextTest.php
index f26b49810d4a9ae516bf357f103574c7a7baaab6..57de914383ca0e7f0c071f9c30a0ffbcc9dbb3f1 100644
--- a/core/modules/system/src/Tests/Mail/HtmlToTextTest.php
+++ b/core/modules/system/src/Tests/Mail/HtmlToTextTest.php
@@ -352,7 +352,7 @@ public function testVeryLongLineWrap() {
 
     $maximum_line_length = 0;
     foreach (explode($eol, $output) as $line) {
-      // We must use strlen() rather than drupal_strlen() in order to count
+      // We must use strlen() rather than Unicode::strlen() in order to count
       // octets rather than characters.
       $maximum_line_length = max($maximum_line_length, strlen($line . $eol));
     }
diff --git a/core/modules/text/text.module b/core/modules/text/text.module
index 0ea98e0e43499bd19e67b040b10288d888af9ea9..02140fe0a01a9ae693653e6d7fa90fbab0a19a37 100644
--- a/core/modules/text/text.module
+++ b/core/modules/text/text.module
@@ -91,7 +91,7 @@ function text_summary($text, $format = NULL, $size = NULL) {
   }
 
   // If we have a short body, the entire body is the summary.
-  if (drupal_strlen($text) <= $size) {
+  if (Unicode::strlen($text) <= $size) {
     return $text;
   }
 
diff --git a/core/modules/user/src/AccountForm.php b/core/modules/user/src/AccountForm.php
index a8f39aa5b34f884c5163b525848b771df37f874a..602f0e715d7497934bb0d3e47ea09478173611c7 100644
--- a/core/modules/user/src/AccountForm.php
+++ b/core/modules/user/src/AccountForm.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\user;
 
+use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Entity\ContentEntityForm;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Entity\Query\QueryFactory;
@@ -379,7 +380,7 @@ public function validate(array $form, FormStateInterface $form_state) {
       //   automatic typed data validation in https://drupal.org/node/2227381.
       $field_definitions = $this->entityManager->getFieldDefinitions('user', $this->getEntity()->bundle());
       $max_length = $field_definitions['signature']->getSetting('max_length');
-      if (drupal_strlen($form_state->getValue('signature')) > $max_length) {
+      if (Unicode::strlen($form_state->getValue('signature')) > $max_length) {
         $form_state->setErrorByName('signature', $this->t('The signature is too long: it must be %max characters or less.', array('%max' => $max_length)));
       }
     }
diff --git a/core/modules/user/src/Plugin/Validation/Constraint/UserNameConstraintValidator.php b/core/modules/user/src/Plugin/Validation/Constraint/UserNameConstraintValidator.php
index 5b788ca7a2d4cf25c3164a6ab08b499717a67198..12d4fa3cc43a17077c3f3376f0f53610343ee837 100644
--- a/core/modules/user/src/Plugin/Validation/Constraint/UserNameConstraintValidator.php
+++ b/core/modules/user/src/Plugin/Validation/Constraint/UserNameConstraintValidator.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\user\Plugin\Validation\Constraint;
 
+use Drupal\Component\Utility\Unicode;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidator;
 
@@ -48,7 +49,7 @@ public function validate($items, Constraint $constraint) {
     ) {
       $this->context->addViolation($constraint->illegalMessage);
     }
-    if (drupal_strlen($name) > USERNAME_MAX_LENGTH) {
+    if (Unicode::strlen($name) > USERNAME_MAX_LENGTH) {
       $this->context->addViolation($constraint->tooLongMessage, array('%name' => $name, '%max' => USERNAME_MAX_LENGTH));
     }
   }
diff --git a/core/modules/user/user.module b/core/modules/user/user.module
index 9c49486f6c87ce379b56efcd2e05a6ff16882531..6d3c6f30dbc47f95c38251eb7a8d6745878f6753 100644
--- a/core/modules/user/user.module
+++ b/core/modules/user/user.module
@@ -556,7 +556,7 @@ function template_preprocess_username(&$variables) {
   // their own shortening logic or add markup. If they do so, they must ensure
   // that $variables['name'] is safe for printing.
   $name = $variables['name_raw'] = $account->getUsername();
-  if (drupal_strlen($name) > 20) {
+  if (Unicode::strlen($name) > 20) {
     $name = Unicode::truncate($name, 15, FALSE, TRUE);
     $variables['truncated'] = TRUE;
   }
diff --git a/core/modules/views/src/Plugin/views/field/FieldPluginBase.php b/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
index eb4372673a9072613d00bb107f9b1b302898ffbf..f13b8dbfc5ea1b7282a4d444082334de8a9e1e51 100644
--- a/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
+++ b/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
@@ -1289,7 +1289,7 @@ public function renderText($alter) {
         $base_path = base_path();
         // Checks whether the path starts with the base_path.
         if (strpos($more_link_path, $base_path) === 0) {
-          $more_link_path = Unicode::substr($more_link_path, drupal_strlen($base_path));
+          $more_link_path = Unicode::substr($more_link_path, Unicode::strlen($base_path));
         }
 
         $more_link = _l($more_link_text, $more_link_path, array('attributes' => array('class' => array('views-more-link'))));
@@ -1705,7 +1705,7 @@ public function adminLabel($short = FALSE) {
    *   The trimmed string.
    */
   public static function trimText($alter, $value) {
-    if (drupal_strlen($value) > $alter['max_length']) {
+    if (Unicode::strlen($value) > $alter['max_length']) {
       $value = Unicode::substr($value, 0, $alter['max_length']);
       if (!empty($alter['word_boundary'])) {
         $regex = "(.*)\b.+";
diff --git a/core/modules/views/src/Plugin/views/filter/InOperator.php b/core/modules/views/src/Plugin/views/filter/InOperator.php
index 07bdf669d4399e21380aaa9716d0f8c961210ab0..51468afa38c41dcf42498fc9a3ee6a81b8868726 100644
--- a/core/modules/views/src/Plugin/views/filter/InOperator.php
+++ b/core/modules/views/src/Plugin/views/filter/InOperator.php
@@ -367,7 +367,7 @@ public function adminSummary() {
           if ($values !== '') {
             $values .= ', ';
           }
-          if (drupal_strlen($values) > 8) {
+          if (Unicode::strlen($values) > 8) {
             $values = Unicode::truncate($values, 8, FALSE, TRUE);
             break;
           }
diff --git a/core/modules/views_ui/views_ui.module b/core/modules/views_ui/views_ui.module
index a6a51e34af88098efdad95d9bfb790ae5530c659..7bf6e7127c5b3683d6f18cd94117b4ebfd3b96e6 100644
--- a/core/modules/views_ui/views_ui.module
+++ b/core/modules/views_ui/views_ui.module
@@ -327,7 +327,7 @@ function views_ui_views_analyze(ViewExecutable $view) {
  * This is often used in the UI to ensure long strings fit.
  */
 function views_ui_truncate($string, $length) {
-  if (drupal_strlen($string) > $length) {
+  if (Unicode::strlen($string) > $length) {
     $string = Unicode::substr($string, 0, $length);
     $string .= '...';
   }