Complex sentence: The European Commissioner for Multilingualism is the member of the European Commission responsible for language policy of the European Union, i.e. promoting multilingualism for the citizens and the institutions of the European Union.
Split into simpler sentences: The European Commissioner for Multilingualism is the member of the European Commission. The portfolio is responsible for language policy of the European Union, i.e. promoting multilingualism for the citizens and the institutions of the European Union.