VATStuff is a UK program, will it be internationalised?

Everything is possible, but in this case it is unlikely.

Understanding, and implementing the different UK VAT options are difficult enough - and even now there has not been sufficient testing or feedback to confirm the VAT calculations are correct. Doing this for other countries as well is beyond my resources.

As this is a GPL program - country specific forks are feasible should anyone want to take that on.