This function is called before loading a URL  to allow you an opportunity to modify the URL.

In the following  example the user is only allowed access to local stored files. If a link to an internet-site is clicked, we want a file "DontDoThis.htm" to be shown.

Similar lines of code could also have been placed in OnBeforeNavigate2 but there is an important difference: OnTranslateUrl is not called when you use Navigate or Navigate2 but only when a hyperlink is clicked. So in this example you could still let a speedbutton call EmbeddedWb1.Go('www.somewhere.com') without  redirecting the user to "DontDoThis.htm".OnUpdateUI

OnUpdateUI is called when the command state is changed and it is time to update toolbar buttons, menus etc.
I always place the UI-updating stuff in  OnCommandStateChanged and have not been able to find situations where one could benefit from using OnUpdateUI instead. OnUpdateUI seems to be called more often then OnCommandStateChanged.

The following sample uses OnUpdateUI to make sure that menu-item 'Copy'  (CopyMenu) is enabled only when text has been selected.