I suspect its a formatting error, as i get the same when i copy/paste your code.
Try this, its working for me in my rule:
(starts_with(http.request.accepted_languages[0],"en") and not starts_with(http.request.uri.path, "/en")) or
(starts_with(http.request.accepted_languages[0],"fr") and not starts_with(http.request.uri.path, "/fr"))