Difference between I can't speak German and I do not speak German?

Hello everybody,

I am new in this web site but I am very excited to be able to participate as I have great passion for languages.
I would like to know the difference when using 'can't' or the present simple in some sentences such as:

- I don't speak German/ I can´t speak German
- I don't remember/ I can't remember

Is any of them better than the other? I think both are correct but I would like to know the nuances these two sentences.

I hope someone can help me.

Thank you!

Welcome.

For the first, it's possible that you know how to speak German and choose not to with "don't." With "can't" you lack the ability, even if if you wanted to. The "can't" version is more natural to my ears.

For the remember pair, there is no practical different in meaning. A person cannot choose to remember (let's leave the psychology of repressed memories out of this), so the possibility of being able to but choosing not to doesn't exist.

It's also possible that one "can't" speak German because of some outside prohibition.

"I can't speak German on the job because my company works only in English."