I had this issue.
I'm from Italy, where we use decimal comma as decimal mark, while in USA you use decimal point.
In Italy we use dd/mm/yyyy date format, while in USA you use mm/dd/yyyy.
So the perfect solution for me was Culture="en-GB", because in Great Britain they use decimal point, but the date is in dd/mm/yyyy format, as I want for my RadDatePicker control, with its calendar.
SQL understands the datetime and Chart represents data very well.

Thanks for all your help.