Hi Philip,
I am not sure I understand this part of your question "does the rating system have to be present and possible to rate?".
You don't need to have anything on the page that enables someone to leave a rating/review in order to use structured markup on those ratings/reviews.
I would recommend using an approach combined with rel-alternate-hreflang to link the various product pages in different languages together.
My approach would be to give the star rating (marked up with http://www.schema.org/AggregateRating) gathered across all reviews for that product (in any language). Then on each different language page I'd show the reviews that are in that language (http://www.schema.org/Review).
I have never handled this exact situation, but that feels like the right way to approach it. What do others think?
-Tom
