How to say in Czech: They speak Serbian fluently.

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

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