I also have made my own google home with an rpi3b and seed 2 speaker board. It works fantastic.... but in english!
I search for locale settings on my rpi to change this in dutch, and everything seems to be well installed... still no dutch!
I also install google assistant (dutch) on my smartphone, with the same google account as on my rpi3b.
And guess, on this device it does speak dutch.
I dont want to speak to my cellphone in my house and still trying to get my rpi3b google home in the right language...
Someone an idea?