diff --git a/includes/language/LanguageConverter.php b/includes/language/LanguageConverter.php
index 694976b06ea..ff6cea0aad2 100644
--- a/includes/language/LanguageConverter.php
+++ b/includes/language/LanguageConverter.php
@@ -286,17 +286,19 @@ abstract class LanguageConverter implements ILanguageConverter {
 	 * @return string The preferred language code
 	 */
 	public function getPreferredVariant() {
-		global $wgDefaultLanguageVariant, $wgUser;
+		global $wgDefaultLanguageVariant;
 
 		$req = $this->getURLVariant();
 
 		Hooks::runner()->onGetLangPreferredVariant( $req );
 
-		// NOTE: For calls from Setup.php, wgUser or the session might not be set yet (T235360)
+		$user = RequestContext::getMain()->getUser();
+		// NOTE: For some calls there may not be a context user or session that is safe
+		// to use, see (T235360)
 		// Use case: During autocreation, UserNameUtils::isUsable is called which uses interface
 		// messages for reserved usernames.
-		if ( $wgUser && $wgUser->isSafeToLoad() && $wgUser->isRegistered() && !$req ) {
-			$req = $this->getUserVariant( $wgUser );
+		if ( $user->isSafeToLoad() && $user->isRegistered() && !$req ) {
+			$req = $this->getUserVariant( $user );
 		} elseif ( !$req ) {
 			$req = $this->getHeaderVariant();
 		}
diff --git a/tests/phpunit/languages/LanguageConverterTest.php b/tests/phpunit/languages/LanguageConverterTest.php
index 4feef7b9f0f..64a76657478 100644
--- a/tests/phpunit/languages/LanguageConverterTest.php
+++ b/tests/phpunit/languages/LanguageConverterTest.php
@@ -19,10 +19,9 @@ class LanguageConverterTest extends MediaWikiLangTestCase {
 	 * @param User $user
 	 */
 	private function setContextUser( User $user ) {
-		// TODO stop using the deprecated global here, and convert
-		// LanguageConverter to use RequestContext or dependency injection
-		global $wgUser;
-		$wgUser = $user;
+		// LanguageConverter::getPreferredVariant() reads the user from
+		// RequestContext::getMain(), so set it occordingly
+		RequestContext::getMain()->setUser( $user );
 	}
 
 	protected function setUp() : void {
@@ -31,8 +30,8 @@ class LanguageConverterTest extends MediaWikiLangTestCase {
 
 		$this->setMwGlobals( [
 			'wgDefaultLanguageVariant' => false,
-			'wgUser' => new User,
 		] );
+		$this->setContextUser( new User );
 
 		$this->lang = $this->createMock( Language::class );
 		$this->lang->method( 'getNsText' )->with( NS_MEDIAWIKI )->willReturn( 'MediaWiki' );