I don't think this is a decent task for an application. You see, the user knows better what culture she or he would prefer to stick with. The system is designed to provide a user some means to do that, what else would one need. The user herself/himself or a system administrator should change such system settings, nobody else.
Would you rather consider changing the culture just for your application? If would be totally transparent and independent from the current system settings.
System.Globalization.CultureInfo culture = new System.Globalization.CultureInfo("fr-FR");
System.Threading.Thread.CurrentThread.CurrentCulture = culture;
System.Threading.Thread.CurrentThread.CurrentUiCulture = culture;
During run rime, you can take the required culture from your application configuration file, provide some UI for selection of the culture by the user, or something like that. That would be much more appropriate.
See also my recent answer to a similar question: Question about convert number format