How to say in Czech: How good is his Dutch?

English
How good is
Czech
Jak dobře umí holandsky?
His Dutch is getting better.
His Dutch is very good.
How do you say that in Dutch?
I do not speak Dutch very well.
You speak Dutch very well.
His native language is Dutch.
Is he learning Dutch on his own?
Dutch is a difficult language.
Dutch is difficult.
He is learning Dutch.

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