This is a common globalization issue. What you have to define is a single culture in which to store the data itself, since you are storing it as a string value. Then, do ALL your data input and handling using that culture. In our code, we have several blocks that look similar to this in order to handle multi-cultural math and data display:
//save current culture and set to english
CultureInfo current = System.Threading.Thread.CurrentThread.CurrentCulture;
System.Threading.Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
//Do Math and Data things
//restore original culture
System.Threading.Thread.CurrentThread.CurrentCulture = current;
This way you can make sure that all the data is handled and stored the same way, regardless of the culture being use to generate or display the data.
Edit
To do the data save, and converting the number to a string, you would do things exactly the same way. While you have the current threads CultureInfo setting as "en-US", the .ToString()
methods from all the numbers will use "." instead of "," for the decimal point. The other way to do it is specify a format provider when calling .ToString().
decimalNumber.ToString(new CultureInfo("en-US"));
This specifies that when you convert the number to a string, use the NumberFormat from the provided culture.