@infograf768 We have this small issue in multilingual installation...

I think I found where the problem lies: /installation/model/languages.php at line 1127 we set 'metadesc' to that value and we should probably set it to a null string.

I'm unsure if what we set at line 1125 for 'metadata' is correct...

In that file we have another small issue: article title is set to the PLG_ARTICLE_BUTTON_ARTICLE localised constant. This might be OK for some languages, but it surely isn't for Italian where the translation is "Collega articolo' ("Link article"). We probably should introduce a new string constant...

I can write a PR for the above, but it must be decided if we want it for 3.4.2 (then no new string constant should be introduced) or for 3.5 (then a new string constant *might be introduced*).

Unrelated, but I can't understand why when performing the "Extra steps: Install languages" the default value for "Activate the multilingual feature:" is "no". Wouldn't it be more logical that the default would be "Yes"?

Nope. Most installs are not multilingual. They are monolingual and default language would be another language than en-GB, the one added to installation.

Agree concerning metadesc. Not
'metadesc' => '{"robots":"","author":"","rights":"","xreference":""}',
but
'metadesc' => '',

Introducing a new string in installation to replace "PLG_ARTICLE_BUTTON_ARTICLE" looks useless as anyway the article created is just a sample and might very soon be edited/replaced.

But we could use: COM_CONTENT_CONTENT_TYPE_ARTICLE instead.
This would make:

        $newlanguage = new JLanguage($itemLanguage->language, false);
        $newlanguage->load('com_content.sys', JPATH_ADMINISTRATOR, $itemLanguage->language, true);
        $title = $newlanguage->_('COM_CONTENT_CONTENT_TYPE_ARTICLE`');

This can be closed as we have a PR (#7281)