Up to iOS 8.x.x Cmd+Space or a dedicated shortcut on my Logitech Type + keyboard for iPad Air 2 used to change the keyboard layout.
From iOS 9.0 and above all that changed.
The new shortcut for changing the keyboard language switched to Ctrl+Space or Shift+Ctr+Space if you have more than two and you want to switch in backward direction, but now all new kind of troubles arised.
The old shortcut on the keyboard now just calls "search" and so does the dedicated "search" button too, so now I have two "search" buttons on the keyboard. Two is better than one you may say!
Also another side effect of this, is that now even Shift by itself changes the language too!!
So you can't type a word starting with a capital letter after switching language, or at least, not until the list of languages disappears from the screen!!!
In the early iOS 9 versions, so did Cmd, Alt and Ctrl along with Shift while the list of keyboads was visible.
On later iOS 9 and iOS 10 versions this was narrowed down only to the Shift key, but the behaviour changed slightly from version to version.
In the late iOS 9 versions Shift would keep cycling through keyboards, and it would reset the timer for showing the list of keyboards on screen, so if you kept pressing within 1 sec the shift key, you could be cycling forever.
iOS 10.1 changed that behavior (not fixed) and now if I was pressing the left Shift I would always select one language, while the right Shift would always Select the other (if I had three, it would always go to the top or the bottom one).
iOS 10.2 beta 1 and 2 kept that behaviour and now i'm on iOS beta 3 and both Shifts are again cycling though all the languages!
And all the above are also tested with my Apple A1314 bluetooth keyboard too, so it's not a Logitech hardware keyboard specific series of bugs.
Please just make the keyboard behave exactly as it does on a Mac and it will be just perfect!
Why does it have to be that hard?