Does really something change if you say we don't speak?
Then it's just "emme puhu" (which can also mean not knowing a language).
"Sorry, we do not speak English"
Should be accepted?
Does it actually mean we can not speak english, even if we know how?
No. :) It means they don't know how to speak English.
If they did know how to speak the language but for some reason couldn't use it, they'd say e.g. "Emme voi puhua englantia".
why not accept Can´t-the contraction
It does now.
I wrote "Excuse me" rather than Sorry. Some English people might even say "Forgive me".