I performed the described actions, but it did not help to solve the problem, but I found the reason.
Translation issue due to incorrect source code in the file “../plugins/masterstudy-lms-learning-management-system/stm-lms-templates/account/private/parts/certificate-list.php”
The file is in the plugin “masterstudy-lms-learning-management-system”, but the source code for translation uses the plugin “masterstudy-lms-learning-management-system-pro” because of this the POT translation template file does not see these strings.
<? php else:?>
<h2 class = "stm-lms-account-title">
<? php esc_html_e ('My certificates', 'masterstudy-lms-learning-management-system'); ?>
</h2>
<div class = "multiseparator"> </div>
<h4 class = "no-certificates-notice"> <? php esc_html_e ('You do not have a certificate yet.', 'masterstudy-lms-learning-management-system-pro')?> </h4>
<h4 class = "no-certificates-notice"> <? php esc_html_e ('Get started easy, select a course here, pass it and get your first certificate', 'masterstudy-lms-learning-management-system-pro') ?> </h4>
<? php endif; ?>
Moreover, there are many such lines with an incorrectly specified plugin. And after removing the “-pro” – in the POT template, the strings are defined after synchronization and can be translated in the masterstudy-lms-learning-management-system plugin.
<? php else:?>
<h2 class = "stm-lms-account-title">
<? php esc_html_e ('My certificates', 'masterstudy-lms-learning-management-system'); ?>
</h2>
<div class = "multiseparator"> </div>
<h4 class = "no-certificates-notice"> <? php esc_html_e ('You do not have a certificate yet.', 'masterstudy-lms-learning-management-system')?> </h4>
<h4 class = "no-certificates-notice"> <? php esc_html_e ('Get started easy, select a course here, pass it and get your first certificate', 'masterstudy-lms-learning-management-system')?> </h4>
<? php endif; ?>