There are people working in offices, in companies full of local colleagues, whose English is still poor. Year after year they carry a quiet sense that their English is not good enough.
Here is why
The assumption is that going to work and talking to people will get you there.
But the question nobody asks is: what do you actually talk about at work?
If your job is moving figures from one column to another, the range of things you need to say is small, and it comes round again and again.
Have you done it? Yes, I've done it. Tomorrow I'll do it.
Extremely basic sentences, recycled for years.
The real problem has not been named
When these people say "I can't speak English", what they mean is: I cannot connect with anyone properly.
They cannot get into deeper subjects. The things Vietnamese friends discuss with each other: family, feelings, what actually matters.
They do not have the vocabulary or the range to meet another person at that level.
What it costs
Someone can work somewhere for ten years and still feel profoundly lonely. Still ring home to Vietnam whenever they need a real conversation.
Because where they live, day to day, they have never connected with anybody past the level of work.
That is not a grammar problem. It is a problem of how much of yourself you can express.