Riesci parlare inglese o altro langue?

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@canaca il verbo potere generalmente non si usa in questo caso.

And also, if you ask someone 'puoi parlare inglese?' it might also sound like a request, as if you're asking them to speak English (i.e. it might be like a colloquial version of 'potresti parlare (in) inglese?'), while if you say 'sai parlare inglese?', you're asking them whether they can speak it or not, and it cannot have a second meaning.

(But if you add the article before inglese, 'puoi parlare l'inglese?' can only mean 'are you able to speak English').

'riesci a parlare' sounds a bit unnatural, and also it gives a nuance as if you think that person isn't supposed to be able to do it.