https://learn.microsoft.com/en-us/dotnet/api/system.windows.input.textcompositionmanager.previewtextinput?view=netframework-4.8.1&viewFallbackFrom=windowsdesktop-9.0
TextCompositionManager.PreviewTextInput Attached Event (System.Windows.Input) | Microsoft Learn
Occurs when a TextComposition is completed.
event systemattachedwindowsinputmicrosoft