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

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

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