Do not and Can not

If you cannot do something, you do not have the ABILITY to do something.

If you can't speak English, you do not know the language. But on the other hand, if you know English, but there are some people with you who do not know it, you don't speak it because to do so would be rude.

So if a native speaker starts to speak English with a person who has never studied English, and knows nothing about speaking English, and understands nothing being said, the non-speaker of English should then say, in idiomatic English:

Sorry, I can't speak English.

or

Sorry, I don't speak English.

???

CJ

I was just using it as an example, since the OP did too.

thank you all for replay

you mean that both is same meanings?

Do not (don't) and can not (can't) are not the same.

Like Barb said, when you can not do something, you lack the ability. And when you do not do something, you have the ability, but you choose not to do it.

what is the difference between don't and can't
for example : i can't speak english and i don't speak english

This is an unfortunate example, because in this case we say "I don't speak English" when we mean "I can't speak English" or "I don't know how to speak English". In other words, there are many cases where the difference between don't and can't is