diff -u b/core/modules/system/src/Form/ModulesListForm.php b/core/modules/system/src/Form/ModulesListForm.php
--- b/core/modules/system/src/Form/ModulesListForm.php
+++ b/core/modules/system/src/Form/ModulesListForm.php
@@ -203,7 +203,7 @@
     $form['modules']['#tree'] = TRUE;
     foreach ($modules as $filename => $module) {
       if (empty($module->info['hidden'])) {
-        $package = ucwords(strtolower($module->info['package']));
+        $package = Unicode::ucwords(Unicode::strtolower($module->info['package']));
         $form['modules'][$package][$filename] = $this->buildRow($modules, $module, $distribution);
       }
     }
diff -u b/core/modules/system/src/Tests/Module/InstallUninstallTest.php b/core/modules/system/src/Tests/Module/InstallUninstallTest.php
--- b/core/modules/system/src/Tests/Module/InstallUninstallTest.php
+++ b/core/modules/system/src/Tests/Module/InstallUninstallTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Module;
 
 use Drupal\Core\Logger\RfcLogLevel;
+use Drupal\Component\Utility\Unicode;
 
 /**
  * Install/uninstall core module and confirm table creation/deletion.
@@ -75,7 +76,7 @@
 
       // Install the module.
       $edit = array();
-      $package = ucwords(strtolower($module->info['package']));
+      $package = Unicode::ucwords(Unicode::strtolower($module->info['package']));
       $edit["modules[$package][$name][enable]"] = TRUE;
       $this->drupalPostForm('admin/modules', $edit, t('Install'));
 
@@ -145,7 +146,7 @@
     //   any errors.
     $edit = array();
     foreach ($all_modules as $name => $module) {
-      $edit['modules[' . ucwords(strtolower($module->info['package'])) . '][' . $name . '][enable]'] = TRUE;
+      $edit['modules[' . Unicode::ucwords(Unicode::strtolower($module->info['package'])) . '][' . $name . '][enable]'] = TRUE;
     }
     $this->drupalPostForm('admin/modules', $edit, t('Install'));
     $this->assertText(t('@count modules have been enabled: ', array('@count' => count($all_modules))), 'Modules status has been updated.');