A few days ago I noticed my keyboard's input language had changed from my preferred UK to the US. I.e. whenever I typed £ I would get the # key and quite a few other irritating anomalies.
After putting up with it for frankly much longer than I needed to I discovered the solution was simple.
I searched under Unity for the Text Entry application.
Unity -> Text Entry
I was then presented with two hotkeys to switch between the input sources as shown below.
