It is, in fact, not limited to the USA. The far majority of the people working on the film are in the UK, as that is where the producers are based, but there are people working on various aspects of the film from quite a few different countries.
At this point though, they are well into post-production work, what with the edit being locked, the score being completed, and lots of the visual effects in the bag as well. So if you are interested in being 'entered' for it, you should mention specifically which area you are interested in, as well as your qualifications and some sort of demo reel, and sent it in an email to: email@example.com
. I don't know that they are still looking to fill any positions, but its worth a shot, anyway.
I'm not sure how they would work to accomodate directors in other countries, unless the directors were willing to travel to the UK for the project, because they (the producers, the FXhome crew) are running a company in the UK, and likely can't really just trip off to another country for a film project. In order to get the project to happen at all, they had to fund it, and build much of the sets themselves, to keep costs down. If they weren't able to work from home, I think the cost would be prohibitive. That being said, their goal from the beginning was to get lots of people involved from the community here, regardless of where they were physically located.