diff --git a/core/modules/aggregator/src/FeedForm.php b/core/modules/aggregator/src/FeedForm.php
index 251bb44..ea6714e 100644
--- a/core/modules/aggregator/src/FeedForm.php
+++ b/core/modules/aggregator/src/FeedForm.php
@@ -29,6 +29,7 @@ public function form(array $form, FormStateInterface $form_state) {
     // @todo: convert to a language selection widget defined in the base field.
     //   Blocked on https://drupal.org/node/2226493 which adds a generic
     //   language widget.
+    // Language module may expose or hide this element, see language_form_alter().
     $form['langcode'] = array(
       '#title' => $this->t('Language'),
       '#type' => 'language_select',
diff --git a/core/modules/block_content/src/BlockContentForm.php b/core/modules/block_content/src/BlockContentForm.php
index 0197f9f..877c180 100644
--- a/core/modules/block_content/src/BlockContentForm.php
+++ b/core/modules/block_content/src/BlockContentForm.php
@@ -109,6 +109,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#type' => 'language_select',
       '#default_value' => $block->getUntranslated()->language()->getId(),
       '#languages' => LanguageInterface::STATE_ALL,
+      // Language module may expose or hide this element, see language_form_alter().
       '#access' => FALSE,
     );
 
diff --git a/core/modules/comment/src/CommentForm.php b/core/modules/comment/src/CommentForm.php
index cc8b9d4..1062358 100644
--- a/core/modules/comment/src/CommentForm.php
+++ b/core/modules/comment/src/CommentForm.php
@@ -167,6 +167,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#type' => 'language_select',
       '#default_value' => $comment->getUntranslated()->language()->getId(),
       '#languages' => Language::STATE_ALL,
+      // Language module may expose or hide this element, see language_form_alter().
       '#access' => FALSE,
     );
 
diff --git a/core/modules/contact/src/MessageForm.php b/core/modules/contact/src/MessageForm.php
index a84fb8e..290ddbf 100644
--- a/core/modules/contact/src/MessageForm.php
+++ b/core/modules/contact/src/MessageForm.php
@@ -103,6 +103,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#type' => 'language_select',
       '#default_value' => $message->getUntranslated()->language()->getId(),
       '#languages' => Language::STATE_ALL,
+      // Language module may expose or hide this element, see language_form_alter().
       '#access' => FALSE,
     );
 
diff --git a/core/modules/language/language.module b/core/modules/language/language.module
index dc242a7..d75d9e8 100644
--- a/core/modules/language/language.module
+++ b/core/modules/language/language.module
@@ -450,6 +450,8 @@ function language_form_system_regional_settings_alter(&$form, FormStateInterface
  * Implements hook_form_alter().
  */
 function language_form_alter(&$form, FormStateInterface $form_state, $form_id) {
+  // Content entity forms may have added a langcode field. But content language
+  // configuration should decide if it should be exposed or not in the forms.
   $form_object = $form_state->getFormObject();
   if ($form_object instanceof ContentEntityFormInterface && isset($form['langcode'])) {
     /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
diff --git a/core/modules/menu_link_content/src/Form/MenuLinkContentForm.php b/core/modules/menu_link_content/src/Form/MenuLinkContentForm.php
index d67c5d1..256b23a 100644
--- a/core/modules/menu_link_content/src/Form/MenuLinkContentForm.php
+++ b/core/modules/menu_link_content/src/Form/MenuLinkContentForm.php
@@ -262,6 +262,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#type' => 'language_select',
       '#default_value' =>  $this->entity->getUntranslated()->language()->getId(),
       '#languages' => Language::STATE_ALL,
+      // Language module may expose or hide this element, see language_form_alter().
       '#access' => FALSE,
     );
 
diff --git a/core/modules/node/src/NodeForm.php b/core/modules/node/src/NodeForm.php
index f9fb2ee..16b1a01 100644
--- a/core/modules/node/src/NodeForm.php
+++ b/core/modules/node/src/NodeForm.php
@@ -114,6 +114,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#type' => 'language_select',
       '#default_value' => $node->getUntranslated()->language()->getId(),
       '#languages' => LanguageInterface::STATE_ALL,
+      // Language module may expose or hide this element, see language_form_alter().
       '#access' => FALSE,
     );
 
diff --git a/core/modules/taxonomy/src/TermForm.php b/core/modules/taxonomy/src/TermForm.php
index b10bccb..2e7097c 100644
--- a/core/modules/taxonomy/src/TermForm.php
+++ b/core/modules/taxonomy/src/TermForm.php
@@ -34,6 +34,7 @@ public function form(array $form, FormStateInterface $form_state) {
       '#title' => $this->t('Language'),
       '#languages' => LanguageInterface::STATE_ALL,
       '#default_value' => $term->getUntranslated()->language()->getId(),
+      // Language module may expose or hide this element, see language_form_alter().
       '#access' => FALSE,
     );