The attributes I originally added are:
- trail_visibility: bad - which means: Path sometimes invisible, route partly pathless; Requirements: Basic skills in orientation
(https://wiki.openstreetmap.org/wiki/Key:trail_visibility)
- sac_scale: demanding_mountain_hiking T3, please see description: https://wiki.openstreetmap.org/wiki/Key:sac_scale
I think these attributes are pretty appropriate. I now added an english translation of my description.