I was playing around with the Datetime.ParseExact method, and it wants an IFormatProvider...
It works inputting null, but what exactly does it do?
Also CultureInfo implements this interface and can be used in your case. So you could parse a French date string for example; you could use
var ci = new CultureInfo("fr-FR");
DateTime dt = DateTime.Parse(yourDateInputString, yourFormatString, ci);