Before the update? During the update?

https://github.com/LimeSurvey/LimeSurvey/blob/master/application/helpers/surveytranslator_helper.php#L1375

Can you set debug=2 and send the whole HTML? We don't have the previous function here.

With 7.3.0 I obtain
Error

Call to undefined function getHtmlLangAttributeValue()

/var/www/limesurvey7/application/views/layouts/header.php(10)

01 <?php
02
03 /*
04 Header of the application
05 Called from renderWrappedTemplate
06 /
07
08 ?>
09 <!DOCTYPE html>
10 <html lang="<?php echo htmlspecialchars(getHtmlLangAttributeValue((string) $adminlang)); ?>"<?php echo $languageRTL;?> >
11 <head>
12 <meta http-equiv="content-type" content="text/html; charset=UTF-8" />
13 <meta http-equiv="X-UA-Compatible" content="IE=edge" />
14
15 <!-- Assets load -->
16
17 <!--
18 Notice to developers :
19
20
21 If you turn debug mode on, the asset manager will be off.
22 If you turn degug mode off, the asset manager will be on.

in /index.php/surveyAdministration/listsurveys
or

/var/www/limesurvey7/application/core/LSETwigViewRenderer.php(690)

678 // (in the future, should be template dependant done via XML file)
679 $aData["aSurveyInfo"] = array_merge($aData["aSurveyInfo"], $oTemplate->getClassAndAttributes());
680
681 $languagecode = App()->getLanguage();
682 if (!empty($aData['aSurveyInfo']['sid']) && Survey::model()->findByPk($aData['aSurveyInfo']['sid'])) {
683 if (!in_array($languagecode, Survey::model()->findByPk($aData['aSurveyInfo']['sid'])->getAllLanguages())) {
684 $languagecode = Survey::model()->findByPk($aData['aSurveyInfo']['sid'])->language;
685 }
686 }
687
688 $aData["aSurveyInfo"]['languagecode'] = $languagecode;
689 / Separate from 'languagecode' since some codes (e.g. 'nl-informal') are not valid values for the HTML lang attribute /
690 $aData["aSurveyInfo"]['htmllanguagecode'] = getHtmlLangAttributeValue($languagecode);
691 $aData["aSurveyInfo"]['dir'] = (getLanguageRTL($languagecode)) ? "rtl" : "ltr";
692
693 if (!empty($aData['aSurveyInfo']['sid'])) {
694 $showxquestions = App()->getConfig('showxquestions');
695 $aData["aSurveyInfo"]['bShowxquestions'] = ($showxquestions == 'show' ||
696 ($showxquestions == 'choose' && !isset($aData['aSurveyInfo']['showxquestions'])) ||
697 ($showxquestions == 'choose' && $aData['aSurveyInfo']['showxquestions'] == 'Y'));
698
699
700 // NB: Session is flushed at submit, so sid is not defined here.
701 if (
702 isset($SESSION['responses' . $aData['aSurveyInfo']['sid']]) &&

in index.php.

The missing function getHtmlLangAttributeValue is in the file
application/helpers/surveytranslator_helper.php

Please check if it is in there. If not then you did not properly update/replace all files in the server.

Thank you for this info. I found the problem and I solved it. have a nice day!