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

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

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