Currently the ZMultilingualString component renders a selector with the list of language codes (and language name in the user's selected language) that comes from the backend in the extWikilambdaEditingData config variable.
We can isolate this front-end component a bit more if we allow it to fetch the dropdown data from an API.
As seen in the API Sandbox we can get all the language codes from /api.php?action=query&format=json&meta=languageinfo, but I haven't found how to get the language names as well, any ideas?