Flex - Error installing languages

First time client, longer time joomla user :-).
Purchase code: (removed for privacy)

If I try to add language (for multilanguage site)at the end of install, template cracks with these two errors:
Notice: Undefined offset: 1 in C:\wamp64\www\Flex\installation\view\languages\tmpl\default.php on line 91 (x ±30 modules)
Notice: Trying to get property ‘image_intro_alt’ of non-object in C:\wamp64\www\Flex\templates\flex\html\layouts\joomla\content\intro_image.php on line 37
This before choosing any language to add. I add the language and install finishes with apparently no problem.
Opening site gives a lot of erros and sometimes, some content appears, other times, site just doenst open.
If I make a clean install, no problem, but when adding languages and activating languages plugins and modules in control panel, I receive lots of errors and usually site cracks.
I’m trying to install Flext template, quickstart with virtuecart on fresh install of Wampserver64
Language trying to add (PT-pt)

Can you help me with this issue?

Thank you in advance.
Best regards
Luis João