[BUGFIX] Change setLanguage to setSiteLanguage in FormsFinisher

Classes/Finisher/Forms/FormsFinisher.php

@@ -135,7 +135,7 @@ class FormsFinisher extends AbstractFinisher {
 		$languageId = GeneralUtility::makeInstance(Context::class)->getPropertyFromAspect('language', 'id', 0);
 		$site = GeneralUtility::makeInstance(SiteFinder::class)->getSiteByPageId((int) $GLOBALS['TSFE']->id);
 		$siteLanguage = $site->getLanguageById($languageId);
-		$mailTemplateService->setLanguage($siteLanguage->getTwoLetterIsoCode());
+		$mailTemplateService->setSiteLanguage($siteLanguage);
 
 		$mailToAddresses = trim((string) $this->parseOption('mailTo'));
 		if ($mailToAddresses !== '') {