Thread.CurrentCulture and Thread.CurrentUICulture

When a thread is started, its UI culture is initially determined by using GetUserDefaultUILanguage from the Windows API. This API gets the user UI language.

When a thread is started, its culture is initially determined by using GetUserDefaultLCID from the Windows API. This API gets the default user locale.

Let us take an example. Assume that CurrentCulture is fr-FR and CurrentUICulture is en-US and now is February 15, 2005. The following code:

string str += DateTime.Now.ToString();
str += Environment.NewLine;
str += DateTime.Now.ToString( Thread.CurrentThread.CurrentUICulture);
str += Environment.NewLine;
str += DateTime.Now.ToString( Thread.CurrentThread.CurrentCulture);

will generate the following string:

15/02/2005 12:42:44
2/15/2005 12:42:44 PM
15/02/2005 12:42:44

So the default ToString method takes Thread.CurrentThread.CurrentCulture.

It's easy to change the CurrentCulture and CurrentUICulture of a thread. The following is an example.

Thread.CurrentThread.CurrentCulture = new CultureInfo( "fr-FR" );

If you modify the CurrentCulture or CurrentUICulture property of a thread, its child threads don't inherent the modification. Remember that, when a thread is started, its UI culture and culture are initially determined by using GetUserDefaultUILanguage and GetUserDefaultLCID.

In a common case, you might want that all your threads use one culture (for example, InvariantCulture) other than default. You should set the culture manually when you create a new thread. You should also set the culture manually before you do things on a thread pool thread.