Perhaps the best and easiest solution would be to bring your own tablet fully stocked with your own selection of movies! In general this is a MUCH better option than relying on the (comparatively) limited selection of inflight movies and TV shows on any carrier.

I can’t vouch for any other services, but Netflix has English language subtitles available and a large selection of their content can be downloaded to your tablet for later, offline viewing.

It also sidesteps the issue of whether KLM’s various IFE systems already have, or could be updated to, have English subtitles on their English language content.