I want to add translations to a Plone 5 site.
I assumed alone.app.multilingual is the way to go, but it does not seem to have a 'language independent' setting like Lingualplone had.
Does this mean I need to translate all content (including images and files) or is there another option.
That is correct. The "only" thing you get at the moment is one shared "Media" folder.
I wonder if you could just add another Language Independent Folder (probably at root level) for your purposes?