Language error on Joomla Flex template

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

For this type of issues you need to hire someone to debugging or ask support from author’s item.

Is not simple to fix without debugging, checking files etc.