What should be done to check the capacity of a 100+ year old wooden floor joist?
That’s a lot of information to review, and I’m American so I don’t know anything about metric, but I’ll try...
Your layout is somewhat different than that shown in the “full report” and picture in Section 1 at Zwae....  There the glass windows are in the same wall as your dormer AND at the same level. However, in your building the dormer is in a wall 90 degrees to the glass walls AND in the roof above the main room.
Be careful of using others reports that are similar and not exact. This could affect your structural design. In this case you have twice the glass in the walls as in the report for the unit at Zwae....
I don’t know if you are located in a high wind area or seismic active area, but if so, you’ll need special connections at each side of your windows and special nailing into your plywood roof sheathing.
Also, Based on the size of the joists and their span, I’d guess they are not more than 4’ (1.2 m) on center. This would be a minimum requirement, because your joists at 4’ on center will only support about 60 lbs. per square foot (Live Load and Dead Load) at that span.
Wood that old has dried out and could have some significant “checking”. This can reduce the joists strength and I’d recommend you visually inspect each joist to insure their integrity.