>>2792043
duolingo is shit and good luck with the tones, you really need to get that irl practice
Have paid tutors on superprof for Mandarin and was fairly happy with it for the price, assume Vietnamese is on there. This is if you are serious about it, practice in your free time then do an hour or two a week with a tutor.
Additional bonus is that's it's usually some cute lass you can chat up.