Fatal error: Uncaught Symfony\Component\Config\Util\Exception\XmlParsingException: [ERROR 522] Validation failed: no DTD found

[e.silva]

Hello! I need help solving a problem. 

I tried to upgrade my Prestashop from 1.7.7.0 to 1.7.8.2 with 1-Click Upgrade addon, and something went wrong. 
After that, all the refreshes on admin/backoffice or website goes to an Internal Server Error (HTTP ERROR 500). 

Checking the "error_log" file, I get this log for both pages:

[22-Dec-2021 23:12:24 UTC] PHP Fatal error:  Uncaught Symfony\Component\Config\Util\Exception\XmlParsingException: [ERROR 522] Validation failed: no DTD found ! (in n/a - line 2, column 68)
[ERROR 73] expected '>' (in n/a - line 67, column 11)
[ERROR 76] Opening and ending tag mismatch: xliff line 2 and xlif (in n/a - line 67, column 11) in DIRECTORY_TO_SITE/vendor/symfony/symfony/src/Symfony/Component/Config/Util/XmlUtils.php:66
Stack trace:
#0 DIRECTORY_TO_SITE/vendor/symfony/symfony/src/Symfony/Component/Config/Util/XmlUtils.php(146): Symfony\Component\Config\Util\XmlUtils::parse('<?xml version="...', NULL)
#1 DIRECTORY_TO_SITE/vendor/symfony/symfony/src/Symfony/Component/Translation/Loader/XliffFileLoader.php(54): Symfony\Component\Config\Util\XmlUtils::loadFile('/home/s001539/d...')
#2 DIRECTORY_TO_SITE/vendor/symfony/symfony/src/Symfony/Component/Translation/Loader/XliffFileLoader.php(42): Symfony\Component\Translation\Loader\XliffFileLoader->extract('/home/s001539/d...', Object(Symfony\Compo in DIRECTORY_TO_SITE/vendor/symfony/symfony/src/Symfony/Component/Translation/Loader/XliffFileLoader.php on line 56

 

I tried to fix it in different ways:

• checked the PHP version and all the extensions
• checked the minimum and recommended versions and extensions with "PHP PrestaShop Info" (phppsinfo.php), and all the items is OK in green color
• downloaded the latest release of Prestashop and updated (and replaced the existing) files by FTP
• executed the "composer upgrade" command to rebuild the vendor folder
• clear the "var/cache/" content

Nothing solved my problem. Any suggestion? 
I would love not to lost all the installation of my website, avoiding to make a new fresh installation on it... 

[e.silva]

SOLVED by replacing the content of /app/Resources/translations/xx-XX (my language) and /app/Resources/translations/default folders.