How to say in Czech: How good is her Vietnamese?

English
How good is
Czech
Jak dobře umí vietnamsky?
Her Vietnamese is getting better.
Her Vietnamese is very good.
Her native language is Vietnamese.
Is she learning Vietnamese on her own?
How do you say that in Vietnamese?
I do not speak Vietnamese very well.
You speak Vietnamese very well.
He is learning Vietnamese.
Is he learning Vietnamese?
Vietnamese is a difficult language.

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