I also have installed Google Keyboard app on my tablet and have selected my main Google account as the sync account. The dictionary was initially empty but I have added some words. I also pressed "Sync now" after adding the words.
I have also installed the Google Keyboard app on my phone and just have also selected the same account as on the tablet and have pressed "Sync now". BUT the dictionary hasn't transferred to my phone.
Any ideas on how to make this will work? Thanks! :)