1.The ASP.NET MVC application's view is using the current UI culture (and in the controller code current culture) for managing the format show and the conversion of DateTime and numbers (integer, float, double) values. So in your case it seems that the current culture is set up for English and this generate exception.
2.In order to solve your problem you should set, in your controller, the correct current UI culture and also current culture values needed like in the next example:
Thread.CurrentThread.CurrentUICulture = new CultureInfo("de-DE");
Thread.CurrentThread.CurrentCulture = Thread.CurrentThread.CurrentUICulture;
PS: If you want to find more details about multilingual in the context of an MVC web application you could read my next article:
MVC Basic Site: Step 1 – Multilingual Site Skeleton[
^] (If you need code for MVC4 get it from the 2nd or 3rd articles from this series.)