diff -u b/core/modules/ckeditor/ckeditor.admin.inc b/core/modules/ckeditor/ckeditor.admin.inc
--- b/core/modules/ckeditor/ckeditor.admin.inc
+++ b/core/modules/ckeditor/ckeditor.admin.inc
@@ -61,7 +61,7 @@
 
   $language_direction = $language_interface->getDirection();
 
-  $build_button_item = function($button, $language_direction) {
+  $build_button = function($button, $language_direction) {
     // Set additional attribute on the button if it can occur multiple times.
     if (!empty($button['multiple'])) {
       $button['attributes']['class'][] = 'ckeditor-multiple-button';
@@ -75,7 +75,7 @@
     // Add language direction property.
     $button['language_direction'] = $language_direction;
 
-    // Check for the image button to be present and convert URI to URL.
+    // Check for the image button to be present and convert file URI to URL.
     if (!empty($button['image']) || !empty($button['image_rtl'])) {
       // The language direction is RTL, check for image_rtl otherwise use the
       // default image button path.
@@ -103,17 +103,17 @@
       });
       foreach ($buttons as $button) {
-        $variables['active_buttons'][$row_number][$group_name]['buttons'][] = $build_button_item($button, $language_direction);
+        $variables['active_buttons'][$row_number][$group_name]['buttons'][] = $build_button($button, $language_direction);
       }
     }
   }
   // Assemble list of disabled buttons (which are always a single row).
   $variables['disabled_buttons'] = array();
   foreach ($disabled_buttons as $button) {
-    $variables['disabled_buttons'][] = $build_button_item($button, $language_direction);
+    $variables['disabled_buttons'][] = $build_button($button, $language_direction);
   }
   // Assemble list of multiple buttons that may be added multiple times.
   $variables['multiple_buttons'] = array();
   foreach ($multiple_buttons as $button) {
-    $variables['multiple_buttons'][] = $build_button_item($button, $language_direction);
+    $variables['multiple_buttons'][] = $build_button($button, $language_direction);
   }
 }
diff -u b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php
--- b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php
+++ b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/Internal.php
@@ -131,157 +131,157 @@
       // "basicstyles" plugin.
       'Bold' => array(
         'label' => t('Bold'),
-        'image_alternative' => 'bold',
+        'internal_button' => 'bold',
       ),
       'Italic' => array(
         'label' => t('Italic'),
-        'image_alternative' => 'italic',
+        'internal_button' => 'italic',
       ),
       'Underline' => array(
         'label' => t('Underline'),
-        'image_alternative' => 'underline',
+        'internal_button' => 'underline',
       ),
       'Strike' => array(
         'label' => t('Strike-through'),
-        'image_alternative' => 'strike',
+        'internal_button' => 'strike',
       ),
       'Superscript' => array(
         'label' => t('Superscript'),
-        'image_alternative' => 'superscript',
+        'internal_button' => 'superscript',
       ),
       'Subscript' => array(
         'label' => t('Subscript'),
-        'image_alternative' => 'subscript',
+        'internal_button' => 'subscript',
       ),
       // "removeformat" plugin.
       'RemoveFormat' => array(
         'label' => t('Remove format'),
-        'image_alternative' => 'removeformat',
+        'internal_button' => 'removeformat',
       ),
       // "justify" plugin.
       'JustifyLeft' => array(
         'label' => t('Align left'),
-        'image_alternative' => 'justifyleft',
+        'internal_button' => 'justifyleft',
       ),
       'JustifyCenter' => array(
         'label' => t('Align center'),
-        'image_alternative' => 'justifycenter',
+        'internal_button' => 'justifycenter',
       ),
       'JustifyRight' => array(
         'label' => t('Align right'),
-        'image_alternative' => 'justifyright',
+        'internal_button' => 'justifyright',
       ),
       'JustifyBlock' => array(
         'label' => t('Justify'),
-        'image_alternative' => 'justifyblock',
+        'internal_button' => 'justifyblock',
       ),
       // "list" plugin.
       'BulletedList' => array(
         'label' => t('Bullet list'),
-        'image_alternative' => 'bulletedlist',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'bulletedlist',
+        'internal_button_has_rtl' => TRUE,
       ),
       'NumberedList' => array(
         'label' => t('Numbered list'),
-        'image_alternative' => 'numberedlist',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'numberedlist',
+        'internal_button_has_rtl' => TRUE,
       ),
       // "indent" plugin.
       'Outdent' => array(
         'label' => t('Outdent'),
-        'image_alternative' => 'outdent',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'outdent',
+        'internal_button_has_rtl' => TRUE,
       ),
       'Indent' => array(
         'label' => t('Indent'),
-        'image_alternative' => 'indent',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'indent',
+        'internal_button_has_rtl' => TRUE,
       ),
       // "undo" plugin.
       'Undo' => array(
         'label' => t('Undo'),
-        'image_alternative' => 'undo',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'undo',
+        'internal_button_has_rtl' => TRUE,
       ),
       'Redo' => array(
         'label' => t('Redo'),
-        'image_alternative' => 'redo',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'redo',
+        'internal_button_has_rtl' => TRUE,
       ),
       // "blockquote" plugin.
       'Blockquote' => array(
         'label' => t('Blockquote'),
-        'image_alternative' => 'blockquote',
+        'internal_button' => 'blockquote',
       ),
       // "horizontalrule" plugin
       'HorizontalRule' => array(
         'label' => t('Horizontal rule'),
-        'image_alternative' => 'horizontalrule',
+        'internal_button' => 'horizontalrule',
       ),
       // "clipboard" plugin.
       'Cut' => array(
         'label' => t('Cut'),
-        'image_alternative' => 'cut',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'cut',
+        'internal_button_has_rtl' => TRUE,
       ),
       'Copy' => array(
         'label' => t('Copy'),
-        'image_alternative' => 'copy',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'copy',
+        'internal_button_has_rtl' => TRUE,
       ),
       'Paste' => array(
         'label' => t('Paste'),
-        'image_alternative' => 'paste',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'paste',
+        'internal_button_has_rtl' => TRUE,
       ),
       // "pastetext" plugin.
       'PasteText' => array(
         'label' => t('Paste Text'),
-        'image_alternative' => 'pastetext',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'pastetext',
+        'internal_button_has_rtl' => TRUE,
       ),
       // "pastefromword" plugin.
       'PasteFromWord' => array(
         'label' => t('Paste from Word'),
-        'image_alternative' => 'pastefromword',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'pastefromword',
+        'internal_button_has_rtl' => TRUE,
       ),
       // "specialchar" plugin.
       'SpecialChar' => array(
         'label' => t('Character map'),
-        'image_alternative' => 'specialchar',
+        'internal_button' => 'specialchar',
       ),
       'Format' => array(
         'label' => t('HTML block format'),
         'button_text' => t('Format'),
-        'image_alternative' => 'format',
+        'internal_button' => 'format',
         'is_dropdown' => TRUE,
       ),
       // "table" plugin.
       'Table' => array(
         'label' => t('Table'),
-        'image_alternative' => 'table',
+        'internal_button' => 'table',
       ),
       // "showblocks" plugin.
       'ShowBlocks' => array(
         'label' => t('Show blocks'),
-        'image_alternative' => 'showblocks',
-        'image_alternative_rtl' => TRUE,
+        'internal_button' => 'showblocks',
+        'internal_button_has_rtl' => TRUE,
       ),
       // "sourcearea" plugin.
       'Source' => array(
         'label' => t('Source code'),
-        'image_alternative' => 'source',
+        'internal_button' => 'source',
       ),
       // "maximize" plugin.
       'Maximize' => array(
         'label' => t('Maximize'),
-        'image_alternative' => 'maximize',
+        'internal_button' => 'maximize',
       ),
       // No plugin, separator "button" for toolbar builder UI use only.
       '-' => array(
         'label' => t('Separator'),
-        'image_alternative' => 'separator',
+        'internal_button' => 'separator',
         'button_text' => t('Button separator'),
         'is_separator' => TRUE,
         'attributes' => array(
diff -u b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/StylesCombo.php b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/StylesCombo.php
--- b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/StylesCombo.php
+++ b/core/modules/ckeditor/src/Plugin/CKEditorPlugin/StylesCombo.php
@@ -60,7 +60,7 @@
       'Styles' => array(
         'label' => t('Font style'),
         'button_text' => t('Styles'),
-        'image_alternative' => 'styles',
+        'internal_button' => 'styles',
         'is_dropdown' => TRUE,
       ),
     );
diff -u b/core/modules/ckeditor/src/Tests/CKEditorLanguageDirectionTest.php b/core/modules/ckeditor/src/Tests/CKEditorLanguageDirectionTest.php
--- b/core/modules/ckeditor/src/Tests/CKEditorLanguageDirectionTest.php
+++ b/core/modules/ckeditor/src/Tests/CKEditorLanguageDirectionTest.php
@@ -33,14 +33,13 @@
   protected function setUp() {
     parent::setUp();
 
-    // Create a Full HTML filter format and associate this with CKEditor.
+    // Create a text format and associate this with CKEditor.
     FilterFormat::create(array(
       'format' => 'full_html',
       'name' => 'Full HTML',
       'weight' => 1,
       'filters' => array(),
     ))->save();
-
     Editor::create(array(
       'format' => 'full_html',
       'editor' => 'ckeditor',
@@ -56,7 +55,7 @@
   }
 
   /**
-   * Tests loading of CKEditor CSS, JS and JS settings.
+   * Tests that CKEditor RTL classes are being added.
    */
   public function testLanguageDirectionChange() {
     $this->drupalLogin($this->admin_user);
@@ -69,7 +68,7 @@
     $edit = array('site_default_language' => 'ar');
     $this->drupalPostForm('admin/config/regional/settings', $edit, t('Save configuration'));
 
-    // Once the language is changed then goto CKEditor Full HTML configuration.
+    // Once the default language is changed, go to the tested text format configuration page. 
     $this->drupalGet('admin/config/content/formats/manage/full_html');
     $this->assertPattern('|cke_rtl|', 'Correct language direction classes are being added.');
   }
diff -u b/core/modules/ckeditor/templates/ckeditor-settings-toolbar.html.twig b/core/modules/ckeditor/templates/ckeditor-settings-toolbar.html.twig
--- b/core/modules/ckeditor/templates/ckeditor-settings-toolbar.html.twig
+++ b/core/modules/ckeditor/templates/ckeditor-settings-toolbar.html.twig
@@ -3,12 +3,12 @@
  * @file
  * Default theme implementation for the CKEditor settings toolbar.
  *
- * This template uses twig macro to create the CKEditor buttons.
+ * This template uses Twig macro to create the CKEditor buttons.
  * @see http://twig.sensiolabs.org/doc/tags/macro.html
  *
  * Available variables:
  * - button: A list containing the CKEditor buttons.
- *   - image_alternative: HTML string representing the contents of this button.
+ *   - internal_button: Indentifier of internal button.
  *   - is_dropdown: Flag for showing a dropdown type button (Optional). If the
  *     value is true then a dropdown button is generated.
  *   - is_separator: Flag for showing a separator "button" (Optional). If the
@@ -29,7 +29,7 @@
 #}
 {% macro button(button) %}
   {# Buttons with text as labels #}
-  {% if button.image_alternative %}
+  {% if button.internal_button %}
     {# Dropdown Buttons. #}
     {% if button.is_dropdown %}
       <a href="#" role="button" title="{{ button.button_text }}" aria-label="{{ button.button_text }}">
@@ -41,7 +41,7 @@
     {# Normal Buttons. #}
     {% else %}
       <a href="#" role="button" title="{{ button.label }}" aria-label="{{ button.label }}" class="cke-icon-only cke_{{ button.language_direction }}">
-        <span class="cke_button_icon cke_button__{{ button.image_alternative }}_icon">{{ button.label }}</span>
+        <span class="cke_button_icon cke_button__{{ button.internal_button }}_icon">{{ button.label }}</span>
       </a>
     {% endif %}
   {# Buttons with image as labels. #}
only in patch2:
unchanged:
--- a/core/modules/ckeditor/src/CKEditorPluginButtonsInterface.php
+++ b/core/modules/ckeditor/src/CKEditorPluginButtonsInterface.php
@@ -45,10 +45,9 @@
    *   - image: An image for the button to be used in the toolbar.
    *   - image_rtl: If the image needs to have a right-to-left version, specify
    *     an alternative file that will be used in RTL editors.
-   *   - image_alternative: If this button does not render as an image, specify
-   *     an HTML string representing the contents of this button.
-   *   - image_alternative_rtl: Similar to image_alternative, but a
-   *     right-to-left version.
+   *   - internal_button: Identifier of internal button.
+   *   - image_internal_has_rtl: Flag indicating whether there's RTL version
+   *     available.
    *   - attributes: An array of HTML attributes which should be added to this
    *     button when rendering the button in the administrative section for
    *     assembling the toolbar.