There is no option to switch between ISO and ANSI because a national layout is either ISO or ANSI, I don’t remember of any one being available in two variants. ANSI is an American standard, used on US keyboards and …I think nothing else?
The choice is between matching the layout of your current keyboard, or use a different one, in which case the markings on the keycaps will not reflect the function of some keys, which you will get used to, after a while, especially if you touch type.
If you don’t care about the Danish layout, and would rather have an English-oriented layout, UK is ISO.
The UI language can be changed to whatever you would like it to be, Windows will download the corresponding package and different users can even have different UI languages. Remember that the login screen defaults to whatever language selected during installation, BUT it can be changed in the Regional, Language and Stuffies settings.
Hope this helps.