>>> [!note] Migrated issue <!-- Drupal.org comment --> <!-- Migrated from issue #3619422. --> Reported by: [danielwirz](https://www.drupal.org/user/3599555) Related to !12 >>> <h3 id="summary-problem-motivation">Problem/Motivation</h3> <p>On a site where the <code>language</code> module is installed but only one configurable language exists (e.g. after removing all but one language), every page that renders the toolbar item for a user with the <code>use toolbar_language_switcher</code> permission crashes with an HTTP 500:</p> <p><code>TypeError: Drupal\language\LanguageNegotiationMethodBase::setCurrentUser(): Argument #1 ($current_user) must be of type Drupal\Core\Session\AccountInterface, null given, called in core/modules/language/src/LanguageNegotiator.php on line 228 (line 52 of core/modules/language/src/LanguageNegotiationMethodBase.php)</code></p> <p><strong>Root cause</strong></p> <p>When a site has only one configurable language, core's <code>\Drupal\language\LanguageServiceProvider::register()</code> does not register <code>language_request_subscriber</code> (it is registered only when <code>isMultilingual()</code> is TRUE). That subscriber is the only code that calls <code>LanguageNegotiator::setCurrentUser()</code>, so the negotiator's <code>$currentUser</code> property remains NULL for the entire request.</p> <p>The <code>language_negotiator</code> service is still registered, however, and its <code>initLanguageManager</code> service call still attaches it to the language manager. <code>RenderBuilder::build()</code> then calls <code>$this-&gt;languageManager-&gt;getLanguageSwitchLinks()</code> unconditionally. <code>ConfigurableLanguageManager::getLanguageSwitchLinks()</code> sees a negotiator is present and calls <code>LanguageNegotiator::getNegotiationMethodInstance()</code>, which does <code>$instance-&gt;setCurrentUser($this-&gt;currentUser)</code> with <code>NULL</code> &rarr; TypeError.</p> <p> The existing single-language guard in <code>RenderBuilder::build() (if ($urls_count &lt; 2) return [];)</code> comes after the <code>getLanguageSwitchLinks()</code> call, so it never runs.</p> <p>This is also the underlying cause of core issue #3270306, which was closed "cannot reproduce" because the crash cannot be triggered with core alone &mdash; core's own <code>LanguageBlock</code> guards against this state via <code>isMultilingual()</code> in <code>blockAccess()</code>.</p> <h4 id="summary-steps-reproduce">Steps to reproduce</h4> <ol> <li>Install Drupal (tested on 11.3.16, PHP 8.3) with the <code>language</code> module and at least two languages.</li> <li>Install toolbar_language_switcher 2.0.0 and grant a role the <code>use toolbar_language_switcher</code> permission.</li> <li>Delete languages until only one remains (site stays "monolingual" with language module installed).</li> <li>Visit any admin page as a user with that permission where the toolbar item is built uncached (e.g. <code>/admin/config/regional/language</code>) &rarr; WSOD / 500 with the TypeError above.</li> </ol> <h3 id="summary-proposed-resolution">Proposed resolution</h3> <p>Return early from <code>RenderBuilder::build()</code> when the site is not multilingual, mirroring what core's <code>LanguageBlock</code> does:</p> <pre>public function build() {<br>&nbsp;&nbsp; if (!$this-&gt;languageManager-&gt;isMultilingual()) {<br>&nbsp;&nbsp;&nbsp;&nbsp; return [];<br>&nbsp;&nbsp; }<br>&nbsp;&nbsp; ...</pre><p> This also saves needless work on monolingual sites. The existing <code>$urls_count &lt; 2</code> check can stay as a secondary guard for the case where negotiation yields fewer than two accessible links.</p>