Older members may remember when this sort of thing was standard practice here in the UK. I used to work for a London firm doing schools. We never used ladders except on the ground floor!!
The technique was known amongst window cleaners as "jumping". Any ledge, horizontal soilpipe or similar was viewed as an acceptable method of access. Lots of schools had ledges that ran all round the outside at each floor level, and we would climb out of a window, work our way all round the building and then back in again. If there was no ledge, we would climb out, shut the window behind us, clean the outside, then climb back in again.
Only on the ground floor, where it was less effort than to climb out would we use a short ladder.
We would never use the guttering, though, as our gutters would never take the weight. Continental gutters tend to be masonry, part of the wall and therefore much stronger than ours. If you could guarantee the gutter was strong enough to take the weight, any British shiner of my generation would have happily used the technique shown here.
Believe it or not, there were very few accidents in those days - everyone knew exactly what they were doing and thought about it beforehand.
I used to clean blocks of flats like this, working my way from balcony to balcony across window ledges.
Wouldn't do it now

. Never mind elf and safety - the memory makes my blood run cold

Cheers,
Ian