a totally legal method of circumventing legislation. if a company wishes to conduct interviews and training in a non-english language, it can. that's why the ad is phrased exactly the way it is. it's not cricket, but it's legal.
That would not stand up in a tribunal and/or court of law. A company CANNOT discriminate against someone because they are 'English speaking'. This company placed a requirement for the person to be 'Polish Speaking', indeed, they had to be 'fluent'. The 1976 Race Relations Act states that
'unless there is a genuine need for a worker to speak a particular language it is against the law to require that they should do so as a condition of employing them.' Now the information we have above is limited but I can't see any reason (other than they only deliver their training in Polish), for a person to be 'Polish Speaking'. Restricting employment to people from one ethnic or national group is illegal unless the job can only be done by someone in that group such as a role that requires cultural sensitivities. Or it could mean using a black actor for a black role. Discrimination is illegal whether or not it is deliberate, what counts is whether (as a result of an employer's actions), you are treated unfavourably because of your race.