re: American vs. British English
As far as I'm aware we use the same naming. I also double checked my naming before posting (always important
) and I didn't notice any differences between how the US and UK named these parts. In truth, I did pay more attention to UK based pages though. Keet agrees with me though, and that is money in the bank! 
For the stringers, in the special case of turn steps=1, the outside stringers at the quarter turn should really be level. For me the nicest look would be to extend the upper flights stringer downwards to the same level at the turns step, so most of the top of the riser is level with the quarter turn step, with just a little triangle where it joins the upper flight. Hopefully that makes sense. Maybe this would be better handled in the "U shaped with top landing" entries. But if so, could we also have a "U shaped with top and bottom landing" option?
And while I'm thinking of things
it would be cool if the settings for the stair are stored in the created object, so you could reopen the dialog, tweak the setting for that stair object, then update/replace it. This would allow easier experimentation. I found it hard to configure an exact 180 degree spiral for example.This one is a real stretch, but here goes: It would be amazing if you could draw lines with a configured height above the steps pitch rising from the noses of the steps. Here's a diagram of the minimum headroom requirement in the UK. Being able to visualise this would really help in redesigning awkward buildings, (i.e. like mine.) This image is from this nice page that summarises the UK regs. From there, another idea would be if the pitch in degrees could be displayed at creation time as it is mandated to be no greater than 42 degrees. Maybe even the ability to set limits on the configured values (or calculated figures) so that the program could warn you if the staircase is not permitted. No collision detection style stuff, just if x < value < y then mark value in red type thing. i.e. our tread depth must be at least 220mm and our riser height can be no greater than 220mm.
Still with me? Looking at that page I have just spotted a possible change in wording. Stair/Tread depth would actually be Going and Step/Riser height would just be Riser. However, I don't think the US use Going, and these are probably less confusing left as Tread depth and Riser height.
