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

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

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