Episode Language Metadata?

Why does language meta data show up for episodes on some series and not others? When I did and advanced search on shows I had previously rated, I narrowed by Japanese and noticed episodes of some shows populated, but not others (ex. Sumo Do, Sumo Don't). I started to edit some episodes to add the information, but I got a warning that this is information that shouldn't normally be added at the episode level if it can be added at the series level. But should it be added at the episode level since the episodes don't show up when you search on that metadata?