Issue #2196901 by divesh.kumar, longwave: Convert all calls & docs references...

Issue #2196901 by divesh.kumar, longwave: Convert all calls & docs references to check_plain() in core to Drupal\Component\Utility\String::checkPlain() in language module.

core/modules/language/language.admin.inc

@@ -5,6 +5,7 @@
  * Administration functions for language.module.
  */
 
+use Drupal\Component\Utility\String;
 use Drupal\Core\Language\LanguageManager;
 
 /**
@@ -273,7 +274,7 @@ function template_preprocess_language_content_settings_table(&$variables) {
           'data' => array(
             '#prefix' => '<label>',
             '#suffix' => '</label>',
-            '#markup' => check_plain($element[$bundle]['settings']['#label']),
+            '#markup' => String::checkPlain($element[$bundle]['settings']['#label']),
           ),
           'class' => array('bundle'),
         ),

core/modules/language/lib/Drupal/language/Form/LanguageFormBase.php

@@ -7,6 +7,7 @@
 
 namespace Drupal\language\Form;
 
+use Drupal\Component\Utility\String;
 use Drupal\Core\Entity\EntityFormController;
 use Drupal\Core\Language\Language;
 
@@ -72,7 +73,7 @@ public function validateCommon(array $form, array &$form_state) {
     if (!isset($form['langcode_view']) && preg_match('@[^a-zA-Z_-]@', $form_state['values']['langcode'])) {
       $this->setFormError('langcode', $form_state, $this->t('%field may only contain characters a-z, underscores, or hyphens.', array('%field' => $form['langcode']['#title'])));
     }
-    if ($form_state['values']['name'] != check_plain($form_state['values']['name'])) {
+    if ($form_state['values']['name'] != String::checkPlain($form_state['values']['name'])) {
       $this->setFormError('name', $form_state, $this->t('%field cannot contain any markup.', array('%field' => $form['name']['#title'])));
     }
   }