The main WPF thread will always be assigned a default setting for CurrentCulture and CurrentUICulture. You can also explicitly set these values based on user preferences (to be discussed). An important point to note, however, is that if a WPF application spins up new threads, those threads will not inherit the main UI thread’s culture settings, in fact they will not be set at all! So, be sure to explicitly assign new threads with the appropriate values.