Occasionally I pair program with a developer who uses a Mac keyboard with his Windows machine. In order to use the Mac keyboard accurately, his default keyboard language is English (US). Although there's also a regular UK windows keyboard plugged in and ready to use, it requires time and effort to navigate the mouse to the language bar and swap to UK layout. This breaks the flow required to successfully pair program.
Good news - the language bar allows keyboard shortcuts to switch between languages. The default key combination SHIFT + LEFT ALT will loop through all the installed keyboard languages, in this instance toggling between US and UK keyboard layouts. But you can also set key combinations that will jump to a specific language.
From the Control Panel or the Start Menu, open the Region and Language settings page, navigate to the Keyboards and Languages tab and click the "Change keyboards" button: