Issue #2313309: Admin toolbar and contextual links should always be rendered in the admin language (if set)

core/lib/Drupal/Core/Cache/Context/AccountAdminLanguageCacheContext.php

+<?php
+
+namespace Drupal\Core\Cache\Context;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Session\AccountProxyInterface;
+
+/**
+ * Defines an AdminLanguageCacheContext service, for "admin language" caching.
+ *
+ * Cache context ID: 'user.admin_language'.
+ */
+class AccountAdminLanguageCacheContext implements CacheContextInterface {
+
+  /**
+   * Constructs a new AccountAdminLanguageCacheContext service.
+   *
+   * @param \Drupal\Core\Session\AccountProxyInterface $currentUser
+   *   The current user.
+   */
+  public function __construct(protected AccountProxyInterface $currentUser) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getLabel(): string {
+    return t("Account's administration language");
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContext(): string {
+    return $this->currentUser->getPreferredAdminLangcode();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheableMetadata(): CacheableMetadata {
+    return new CacheableMetadata();
+  }
+
+}