How to say in Czech: Their native language is Russian.

English
native language is
Czech
Jejich rodný jazyk je ruština.
Russian is a difficult language.
What is their native language?
How good is their Russian?
Their Russian is getting better.
Their Russian is very good.
Are they learning Russian on their own?
He is learning Russian.
He is not Russian.
He is Russian.
Is he learning Russian?

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