When needsInputModeSwitchKey is false, your custom keyboard is supposed to hide the 'switch keyboard' button. This is false on iPhone X because the globe button is provided by the system. However it is also false when running an app in compatibility mode - not optimized for iPhone X - and here it falls back to the non-iPhone X keyboard inside the compatibility window. This results in there being no globe key visible, it's impossible to switch keyboards.
I filed this bug report: rdar://35549038
Are there any workarounds? Any suggestions, other than show the duplicate globe button for iPhone X until this issue is addressed?
The issue continues to occur with iOS 11.2 beta 3. When can we expect this to be fixed?