NopDatePicker should show CultureSpecific Year, and store CultureInvariant as a value in db,

in NopDatePicker the code that fills the dropdownlist should change like this:

for (int i = this.LastYear, j = this.LastYearByCulture; i >= this.FirstYear; i--, j--)
            {
                ListItem tempItem = new ListItem();
                tempItem.Text = j.ToString();
                tempItem.Value = i.ToString();
                lstYears.Items.Add(tempItem);
            }

and a new property could be used:

public int LastYearByCulture

which by "get" should return:

Thread.CurrentThread.CurrentCulture.Calendar.GetYear(DateTime.Now);
(LastYear returns DateTime.Now.Year)

(for most cultures that use Gregorian calendar it's not needed, but it should be to support all cultures)