MIUI 7/8 has no way to disable the global Google Spell Check

I am the happy owner of a brand new Xiaomi Redmi 3 Prime. It comes with the MIUI 7, and there is a free upgrade to MIUI 8 via the built-in upgrade software. My only complaint, so far, is that it comes with a utterly annoying spell checker that applies globally to all text inputs, and has no user-friendly way to disable it, as you'll see in the following link. As I found out, this is a problem in the MIUI system. I've tried all the solutions from this thread , but to no avail: * Trying to set the spell_checker_enabled to 0 requires su, and it says su couldn't be found, either from Terminator Emulator for Android and from ADB remote shell. * Trying to set the Google Keyboard language to QWERTY worked, untill I decided to disable this Keyboard, because I won't be using it. * Disabling Google Keyboard Autocorrection doesn't work. * In the Google Keyboard app detail from system configuration, it doesn't let me disable it. Would be really glad to disable it. Side note: this is irrelevant to this question, but as I tried to install minimal ADB and Fastboot on my Ubuntu, it suggested me to run apt-get -f install because there were unmet dependencies. After I did it and rebooted my laptop, my graphical UI was broken and I've just installed a fresh Ubuntu on it.