I would not want to receive blood from someone who could not have been screened thoroughly because they were not able to communicate in local (here, Polish then) language.
Even if they could not communicate effectively, screening tests are pretty thorough, at least in the UK, and I can't imagine Poland not screening for the same diseases/viruses the UK does.
If someone turned up to donate blood without being able to speak Polish, also presuming that a person would not be able to complete necessary paperwork, I am sure blood would not be taken.
This is what blood is screened for in the UK :
blood.co.uk/resources/leaflets/tests-on-your-blood