This thread is resolved. Here is a description of the problem and solution.
Problem: An error of type E_ERROR was caused in line 26 of the file /wp-content/plugins/sitepress-multilingual-cms/classes/templates/wpml-twig-template-loader.php. Error message: Uncaught Error: Class 'Twig_Loader_Filesystem' not found in /www/vivantica_823/public/wp-content/plugins/sitepress-multilingual-cms/classes/templates/wpml-twig-template-loader.php:26
Solution: User was missing a file or a part of file in the main WPML plugin. Delete the current WPML Sitepress Multilingual CMS (deleting it won't delete your translations. Translations are in database.) Download a fresh copy from https://wpml.org/account/downloads/ Install and activate.
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