Let me start with I have never written an International app but have bumped into the problem before (about 10 years ago). I had a client who was in the upper thumb of MI who occasionally had Canadian customers. I stored the Zip code in US format and he couldn't enter his postal codes for these customers. To fix it would have required a special version for him (NEVER) or a converting everyone else (60+). I told him it would be in the next update but that was 8 months later and we lost him as a customer. Because of this, I use R and store data unformatted.