The CultureInfo class

When it comes to localization of your application, especially one class is of great importance: The CultureInfo class from the System.Globalization namespace. From this class, you can get information about pretty much every possible culture out there, including a wide range of culture specific settings. The CultureInfo class can really help you when localizing your webpages, most notably because ASP.NET will keep a reference to the specific CultureInfo instance related to a specific visitor. Does it sound complicated? Let me show you a little example:
<%@ Page Language="C#" Culture="Auto" %>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>CultureInfo demo</title>
</head>
<body>
    <form id="MainForm" runat="server">
        <% Response.Write("Your current culture: " + System.Globalization.CultureInfo.CurrentCulture.DisplayName);    %>
    </form>
</body>
</html>
Try running this and you will get a culture related to you - but how? Actually, since the Culture property of the Page directive is set to Auto, this is controlled by your browser. Most browsers allow you to set your favorite languages, and from that, ASP.NET tries to detect which culture to use for you. We will look into that in greater detail later on. Your current culture is used in lots of cases, for instance when formatting dates and numbers, since that varies from culture to culture. Now, you may want to use a specific culture, no matter what your visitors browser tells you. In that case, you can set the Culture property of the page, like this:
<%@ Page Language="C#" Culture="en-US" %>
If you run the example now, you will get the output "English (United States)", which is the language of English, with a specific US culture. English comes in other flavors too, for instance British or Australian. en-US is considered a specific culture, where en (just English) is considered a neutral culture, since it's just a language, not specific to any country. Now, to see the difference between two cultures, try running this example:
<%@ Page Language="C#" Culture="en-US" %>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>CultureInfo demo</title>
</head>
<body>
    <form id="MainForm" runat="server">
        <% Response.Write("Current date, in a culture specific format: " + DateTime.Now.ToString()); %>
    </form>
</body>
</html>
Now, try changing the page Culture to a German one, like this:
<%@ Page Language="C#" Culture="de-DE" %>
You will see the exact same line of code output a different result, because it's culture dependant. But you can actually output a culturally aware date (or number or anything else) without changing the culture of the page. For instance, like this:
<% Response.Write("Current date, in a culture specific format: " + DateTime.Now.ToString(System.Globalization.CultureInfo.GetCultureInfo("de-DE").DateTimeFormat)); %>
We simply get a reference to a German culture, and then use it as a parameter to the ToString() method on the DateTime class. CultureInfo comes with a NumberFormat property for formatting numbers too. Obviously, formatting dates and numbers is just a small part of localizing an application, but the CultureInfo class is (or at least can be) the foundation of this process, mainly because it's so well integrated with the .NET framework, and in particular ASP.NET.

Culture vs. UICulture

This was all about the Culture property, but the Page class does come with another related property: The UICulture property. UI stands for User Interface, so in fact, this is the property we can use to identify the language used for the visual part of the page, while the Culture property is used for the non-UI stuff, like date and number formatting, sorting and so on. In lots of situations, you would want to use the same Culture and UICulture, but there are cases where you would want to separate these two, for instance when you want the text of a website to be localized, while still outputting a consistent date or number format, no matter where the user comes from.
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