Yes, that works. If you press the key where äöü would be in a German game, it still writes äöü (at least in Fortnite). But you must have a Razer keyboard.

Yes, they fit all keyswitches with a cross and the Razer Ornata V3.

According to the official answer, yes, but we recommend asking this in a discussion, as experience has shown that you will get more answers there than with a single question.

Yes, it should, since this is a kit with 128 keys compatible with ISO and ANSI. The right part uses 1u keycaps on the AKKO so you can use the same keycaps as you would on a Blackwidow v3 Mini.

No, they are not recognisable.

Yes, they work. However, the keycaps are in the US/UK layout.

We have reported the error on our website.

The keycap upgrade sets are each in the US/UK layout.