Bug in MetaWizard widget

Steps to reproduce:

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When deleting the recently added language, a JS error is thrown.

Cause: The metaDelete() method in core.js tries to re-enable the language in the select field:

core-bundle/src/Resources/public/core.js

Line 2329 in df6731c

    
           opt.getElement('option[value=' + li.getProperty('data-language') + ']').removeProperty('disabled');

But the select field does not contain (disabled) language options of currently used languages.

Maybe the language should not be removed from the select field:

core-bundle/src/Resources/contao/widgets/MetaWizard.php

Line 166 in df6731c

unset($languages[$lang]);

But instead the active languages should be added with the "disabled" attribute to the select:

core-bundle/src/Resources/contao/widgets/MetaWizard.php

Line 179 in df6731c

$options[] = '<option value="' . $k . '">' . $v . '</option>';

Maybe something like this (totally untested):
$options[] = '<option value="' . $k . '"' . ($this->varValue[$k] ? ' disabled="disabled"' : '') . '>' . $v . '</option>';
and removing the unset()

Moved to contao/contao