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

English
How good is
Czech
Jak dobře umějí holandsky?
Their Dutch is getting better.
Their Dutch is very good.
How do you say that in Dutch?
I do not speak Dutch very well.
You speak Dutch very well.
Their native language is Dutch.
Are they learning Dutch on their own?
Dutch is a difficult language.
Dutch is difficult.
He is learning Dutch.

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