This was happening to me in VS 2010, despite not using R#. After digging through those links @Ryan Spears put in his post I have come across a permanent solution Source. (Note that @Maffelu’s solution did work for me, but it can switch back if I accidentally hit Left Alt + Shift).
This is also weird because Left Alt + Shift doesn’t seem to change it back, so you have to go to the source: a key binding buried in the Windows Control Panel:
Control Panel > Region and Language > Keyboards and Languages > Change Keyboards > Advanced Key Settings > Change Key Sequence > Select “Not Assigned” for both Switching Input Language and Switch Keyboard Layout.
via Stack Overflow.