[entity:language] tokens throw InvalidArgumentException for content entities without a langcode field

Problem/Motivation

TokenTokenInfoHooks::tokenInfoAlter() automatically registers a language chained token ([entity_type:language:*]) for every content entity token type that doesn't already define its own.

This registration does not check whether the entity type actually has a langcode field. When the token is resolved, TokenTokensHooks::tokens() reads the field directly instead of using the entity's \Drupal\Core\Entity\EntityInterface::language() method.

Not every content entity is required to declare a langcode entity key / base field - it's entirely valid for a simple, non-translatable content entity to omit it. For such entities this throws:

php.ERROR: InvalidArgumentException: Field langcode is unknown. in Drupal\Core\Entity\ContentEntityBase->getTranslatedField() (line 630 of /var/www/html/web/core/lib/Drupal/Core/Entity/ContentEntityBase.php).

Note that for the field tokens it is already using this method for getting a proper language instead of direct access: TokenTokensHooks::fieldTokens()

Steps to reproduce

1. Define a content entity type that does not declare a langcode entity key
2. Save an instance of this entity.
3. Resolve any token from its token tree that touches the auto-registered language sub-tree, e.g:
   

   <?php
   
   use Drupal\module\Entity\MyEntity;
   use Drupal\Core\Render\BubbleableMetadata;
   
   $entity = MyEntity::load(1);
   $replacements = \Drupal::token()->generate(
     'my_entity',
     ['language:langcode' => '[my_entity:language:langcode]'],
     ['my_entity' => $entity],
     [],
     new BubbleableMetadata(),
   );
   

   This also happens implicitly when eagerly resolving a full token tree with
   'values' => TRUE via TreeBuilder::buildTree() (e.g. any token browser/preview UI built on top of Token module).

4. Field langcode is unknown. is thrown.

Proposed resolution

Replace the direct field access with the entity's own language method:

$language_options = array_merge($options, [
  'langcode' => $entity->language()->getId(),
]);

Remaining tasks

User interface changes

API changes

Data model changes