(I hope I'm correct here an this is not (purely) a transitous property.)
It appears that the Motis 2 plan response is (with some deviations) modeled after the old OTP REST plan response.
With OTP, the route name that is displayed is typically returned in the property leg.routeshortname.
in OTP, Urban modes this routeshortname typically consists if typically 1-3 characters without a mode name (like S1 or U5 or 44).
For trains, typically an abbreviation of the train type is added (like IC 217)
(for more talkative names, OTP returns routelongname)
In this routing example from Amsterdam Airport to Rijksmuseum,

Metro 52 routehortname appears to contain something like a trip id. This makes not much sense.
That the short name contains mode descriptions like "Bus" and "Tram" is very unusual and debatable, especially since there is a separate property for mode.
For "Intercity 3555" I would expect "IC 3555" in routeshortname.
Maybe there is a better way what to map into routeshortname?
There is always the possibility to fill leg.routelongname, if somebody wants it.
(I hope I'm correct here an this is not (purely) a transitous property.)
It appears that the Motis 2 plan response is (with some deviations) modeled after the old OTP REST plan response.
With OTP, the route name that is displayed is typically returned in the property leg.routeshortname.
in OTP, Urban modes this routeshortname typically consists if typically 1-3 characters without a mode name (like S1 or U5 or 44).
For trains, typically an abbreviation of the train type is added (like IC 217)
(for more talkative names, OTP returns routelongname)
In this routing example from Amsterdam Airport to Rijksmuseum,

Metro 52 routehortname appears to contain something like a trip id. This makes not much sense.
That the short name contains mode descriptions like "Bus" and "Tram" is very unusual and debatable, especially since there is a separate property for mode.
For "Intercity 3555" I would expect "IC 3555" in routeshortname.
Maybe there is a better way what to map into routeshortname?
There is always the possibility to fill leg.routelongname, if somebody wants it.