How to say in Czech: Are they learning Croatian on their own?

English
Are learning on their own?
Czech
Oni se učí chorvatsky jako samouk?
Are they learning Croatian?
They are learning Croatian.
Where did they learn Croatian?
How good is their Croatian?
Their Croatian is getting better.
Their Croatian is very good.
Their native language is Croatian.
Are they Croatian?
They are Croatian.
They are not Croatian.

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