var myCulture = new GC.Spread.Common.CultureInfo();
myCulture.currencySymbol = ""
myCulture.numberDecimalSeparator = ",";
myCulture.numberGroupSeparator = ".";
myCulture.arrayGroupSeparator = ";";
myCulture.listSeparator = ",";
myCulture.amDesignator = "";
myCulture.pmDesignator = "";
myCulture.abbreviatedMonthNames = ["Jan", "Feb", "Mrz", "Apr", "Mai", "Jun", "Jul", "Aug", "Sep", "Okt", "Nov", "Dez", ""];
myCulture.abbreviatedDayNames = ["So", "Mo", "Di", "Mi", "Do", "Fr", "Sa"];
myCulture.abbreviatedMonthGenitiveNames = ["So", "Mo", "Di", "Mi", "Do", "Fr", "Sa"];
myCulture.dayNames = ["Sonntag", "Montag", "Dienstag", "Mittwoch", "Donnerstag", "Freitag", "Samstag"];
myCulture.fullDateTimePattern = "dddd, d. MMMM yyyy HH:mm:ss";
myCulture.longDatePattern = "dddd, d. MMMM yyyy";
myCulture.longTimePattern = "HH:mm:ss";
myCulture.monthDayPattern = "dd MMMM";
myCulture.monthNames = ["Januar", "Februar", "Mrz", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember", ""];
myCulture.monthGenitiveNames = ["Januar", "Februar", "Mrz", "April", "Mai", "Juni", "Juli", "August", "September", "Oktober", "November", "Dezember", ""];
myCulture.shortDatePattern = "dd.MM.yyyy";
myCulture.shortTimePattern = "HH:mm";
myCulture.yearMonthPattern = "MMMM yyyy";

//add one culture
GC.Spread.Common.CultureManager.addCultureInfo("de-DE", myCulture);
//switch to "de-DE" culture
GC.Spread.Common.CultureManager.culture("de-DE");
var d = new Date();
//With culture
activeSheet.setValue(1, 0, new Date(d.setDate(d.getDate() + 1)));
activeSheet.getCell(1, 0).formatter("mmm");
var dvalue = 12345.6789;
var nvalue = 12345;
activeSheet.setColumnWidth(0, 100);
activeSheet.setColumnWidth(1, 100);
activeSheet.setColumnWidth(2, 100);
activeSheet.setValue(0, 0, dvalue);
activeSheet.getCell(0, 0).formatter("###,###.00");
//Without culture
activeSheet.setValue(2, 0, new Date(d.setDate(d.getDate() + 1)));
//With culture
activeSheet.getCell(3, 0).formatter("yyyy/mmm/dddd");
activeSheet.setValue(3, 0, new Date());