How to say in Czech: Is he learning Vietnamese on his own?

English
Is learning on his own?
Czech
On se učí vietnamsky jako samouk?
He is learning Vietnamese.
Is he learning Vietnamese?
Where did he learn Vietnamese?
His native language is Vietnamese.
His Vietnamese is getting better.
His Vietnamese is very good.
How good is his Vietnamese?
Does he speak Vietnamese?
He does not speak Vietnamese.
He does not speak Vietnamese very well.

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