I saw some posts about how challenging it is to learn Vietnamese. I've been using Pimsleur audio program. I'm a former language teacher and I think this program is fantastic. I tried some books but so far Pimsleur has been the best. Vietnamese tones are more complex so book learning Vietnamese is challenging. I listen to the audio at 65%. I repeat sections frequently. You can get Pimsleur through their website. I use it through my library. Practice daily. I'm a nerd and listen (and speak to self) at the gym. Also, Michigan State has an excellent open source (free) textbook to learn Vietnamese. It's not too mobile friendly. But if you want a quality free resource, start there. I'll put the link in comments. I've never been to Vietnam but it's my next destination.