US, unfortunately. I'm not convinced of the accuracy of the script's list of commonwealth countries. I could have sworn Canada was part of the commonwealth.
https://en.wikipedia.org/wiki/Member_states_of_the_Commonwea...
https://en.wikipedia.org/wiki/Member_states_of_the_Commonwea...
The key cases I think are cheque (vs. check), colour (vs. color), and neighbour (vs. neighbor) and "fuck" is none of those.
Or you could sign up for an open source account at http://crowdin.net/ and just let us do it ourselves.