Federico Viticci writes for Mac Stories:
I see two possible solutions: either Apple implements something close to Ling’s idea with separate shortcuts for frequent and occasional keyboards, or, even better, they build a smarter, unified keyboard that automatically recognizes multiple languages at a time (though that obviously wouldn’t work for Chinese and other non-QWERTY keyboards).
I seriously only see one solution, Apple implements a keyboard that recognize the language in which you are tying. Blackberry did it in 2013!
They added a keyboard in BB10 that understands when you type and can automatically switch languages. Check out the keynote address of the launch. Look at the 24m mark.
I don’t think another button is the good idea. Apple should just make the keyboard work great for multilingual users by enhancing its predictive capabilities in understanding what language is being typed in.