I believe, it should be possible to create the overriding path manually with BTreeFolder2 and File objects through ZMI at
portal_resources/resource_overrides/manage
into
portal_resources/resource_overrides/static/components/tinymce-builded/js/tinymce/langs/it.js
And you should be able to confirm if it works by refreshing ++plone++static/components/tinymce-builded/js/tinymce/langs/it.js
.