I took some help from MSDN, but this is my answer:
double number;
string localStringNumber;
string doubleNumericValueasString = "65.89875";
System.Globalization.NumberStyles style = System.Globalization.NumberStyles.AllowDecimalPoint;
if (double.TryParse(doubleNumericValueasString, style, System.Globalization.CultureInfo.InvariantCulture, out number))
Console.WriteLine("Converted '{0}' to {1}.", doubleNumericValueasString, number);
else
Console.WriteLine("Unable to convert '{0}'.", doubleNumericValueasString);
localStringNumber =number.ToString(System.Globalization.CultureInfo.CreateSpecificCulture("de-DE"));