I myself am a Vietnamese who has been living in the Western world (Hungary, the US, Malta, and coming to France) for the last 9 years, so I guess I can share a bit of my own experience
I totally agree with SteveandMarty that having Vietnamese, or most of the Asian language as mother tongue is not really an advantage in term of learning or more exactly, acquiring other language of the Western world. However knowing and being fluent in English does help tremendously in exchanging languages, as the majority of people in the Western world can speak English well, even though most of the time it will not be their preference language
I have experiences in learning Hungarian (as school compulsory), German (as my own interests), Maltese (work requirements), French (life essential ). I’ll be honest that not all of them turned out well
Hungarian and Maltese were the most difficult as they have nothing to do with any of the languages I’ve ever known. Time didn’t allow me to focus, and the resources are not as many as other languages. What I see is that Turkish acquires Hungarian very fast, and Arabic people can understand and speak Maltese almost right after the first lesson, as those languages shared the same root
German and French were better as they have a lot in common with English, only with more complicated tenses and grammar. I find that if you start first with German or French, then English, it’s much easier. I started with some free applications or wEbsite to have an idea, then go to a language center, took the test to see my level, and then took the intensive class from that level to properly organize what I have known, and got the chance to actually understand and practice the language.
The German and French friends I have can speak English, so it’s not difficult for me to exchange ideas by trying to attempt the target language first, then on the way just ask “Wie sagt man ...(English word or phrases)... auf Deutsch?” or « Comment dit-on...(English phrase)... en Français ? »
That’s all I have to share. Just take it as a grand of salt since I am not fluent as I wish in any of them. Beside German and French being from my own interests (hence I can speak more coherently !!!), other languages were the compulsory parts of a certain periods of my life. If there’s anything to suggest, I would say languages need practice, you need to use them to remember them. Take one or two proper classes as you will learn how the language was constructed and understood its origin (that part is not taught from the free online app). Speak to people, use English as your advantage to get help and find good resources to study
Hope your Expat journey soon starts with great experiences