If you don’t like learning new language, then no one can force you to do that. But if you are working or studying in Vietnam, learning vietnamese is very important.
The difference between foregner who can and can not speak local languages is huge, especialy in Vietnam, you will surprise people if you can speak vietnamese fluently, And most of your work will become smoothier.
You should self-motivated: Even Vietnasmese is not a hard language, but like any other language, learning is not something that easy, and if you dont self-motivated enough, you will give up very soon.
Time and patient, just like self-motivated, you need time learn any seconday language, and ofcourse, if you are not patients then you will never learn anything.