Kati

In my opinion, this name sounds a bit childish in Finnish and is better when used as a nickname only.
Kati in English, however, is an awful spelling error that is tacky even as a nickname.

Kati is way better than Katie, Katy, Kaytie or Catie. I love it as Kati-Louise, it just flows well.

I like the spelling of Kati, it's really sweet and cute. My name is Katie, but I do like my spelling a bit more.