How to say in Czech: They speak Vietnamese fluently.

English
speak fluently.
Czech
Oni mluví plynně vietnamsky.
Do they speak Vietnamese?
They do not speak Vietnamese.
They do not speak Vietnamese very well.
They speak only a little Vietnamese.
They speak Vietnamese.
They speak Vietnamese very well.
Does anybody here speak Vietnamese?
Are they learning Vietnamese?
Are they learning Vietnamese on their own?
They are learning Vietnamese.

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