Given that prototype code has a way of becoming ship code and that one usually doesn't have a whole lot of time to play with a prototype, should one take the time to "do it right" or just mock up as many features as you can in your timeframe? 
Hard-coding resource strings:  yes or no?
Globalization: yes or no?
Performance investigation:  yes or no?
What is the priority list of things to do right in a prototype?