Their English didn't help, but the prominence given to it seems to me to be a product of the xenophobia of certain sections of the British media - an opportunity for the Torygraph to indulge in more Pole-bashing.
It does seem to me that the crew could be criticised for not declaring an emergency, but it doesn't take much English to say 'MAYDAY' so I don't think this was a language competence problem.
I also note that ATC on a couple of occasions said 'one eighty' or 'one hundred and eighty' rather than 'one eight zero', which may not have helped the crew's understanding.