Depends on which part of Poland. Android is right that the Cambridge CELTA the "Trinity College" certificate are better recognised and accredited. You might need one of these to work for the British Council or any half decent school in the UK, maybe in Europe, and a relative handful of other schools around the world (the ones which just so happen to run these courses). Otherwise no one will give a crap whether you have a cert or not, and some volunteer teaching would probably be cheaper and give you more experience.