Using a button for in-progress feedback

An effective way to let users know a process is in progress is to use the button they just clicked.

Here is the initial button state on freetranslation.com:

And here is the button state when clicked, while the translation is in progress:

This approach has two great advantages:  it gives the user feedback right where they gaze is currently fixed (on the button they just clicked)--and, by disabling the button, it prevents users from clicking the button twice (which might happen if they think "nothing" is happening).