27% is good. keep it up! I tried Spanish on there too to brush up on mine, even tho its my first language i've forgotten a lot since i don't speak it much. only with my parents and extended family, but i don't see them much. The Spanish on duolingo is Spaniard so it's a little different from what we speak south of the border. Not much, but some words differ.
Also I didn't know that about the Vietnamese part of the app, I hope my Portuguese sentences aren't wonky.
And don't give up, by the end, you'll count like a native Japanese 8)