Column sort by German date 20.04.2014

Hello
I would like to show a german date in a second column. The date is shown in a German format with dots.
I have aaSorting like this;

"aaSorting": [[ 1, "desc" ]],

but the date is not sorted correct.
30.04.2014
22.04.2014
21.02.2014
20.04.2014
20.03.2014

I have seen that there is a parameter "sType", I tried is like this:

{ "mData": "projectday",
"sWidth": 80,
"sType": "date"
},

But the sort order is still not correct.

thanks for any help

best regards
Hawk