Sale has ended but you can still get this app.
Download Input Switcher Prime Now

Official Description

Input Switcher creates an on-screen floating icon, letting you switch between input methods anywhere anytime. No matter what input method you use, you can switch to another by simply touch the floating icon created by the app. I believe this app should be useful for you If you are using multiple input methods and switch between them frequently.

Prime Version Features:
-Auto hides floating icon when you are not using any keyboards(Need Android 5.0+).
-Set different positions for Landscape and Portrait mode.
-Ads free.
-New features coming soon.


Free Version:
https://play.google.com/store/apps/details?id=com.Melee.keyboardswitcher

Free Version Features:
-One touch on floating icon to switch between input methods.
-Floating Icon can be moved to anywhere you want.
-Auto start when booting up.
-Two types of floating icons for your choice.

Release Note:
Version 1.3
Added a crash reporting system.

Version 1.2.3
A bug caused by Android 6.0 permission management has been fixed.

Version 1.2.2
Minor Bug Fixed.
Thank Mark for reporting it.

Version 1.2.1
Minor Bug Fixed

Version 1.2
Now you can set different positions for landscape and portrait mode.

Version 1.1
1. New UI Added
2. Animation Added when creating and destroying floating windows
3. You can now change the floating icon size

Version 1.0.1
Minor Bug Fixed

Version 1.0
First release of Prime version