"horse.land" subtitle doesn't have translation strings

When a horse hits the ground, the subtitles show "subtitles.entity.horse.land" instead of something that's proper and understandable, such as "Horse lands."

To reproduce

1. Turn on subtitles.
2. Tame a horse, and put a saddle on it.
3. Ride the horse - Jump at least 1-2 blocks high with your horse.
   →  Subtitles say "subtitles.entity.horse.land" when the horse hits the ground.