query: PREFIX wikibase: <http://wikiba.se/ontology#>
  PREFIX wd: <http://www.wikidata.org/entity/> 
  PREFIX wdt: <http://www.wikidata.org/prop/direct/>
  PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
  
  SELECT ?player (GROUP_CONCAT(?nationality;separator=" und ") as ?list)
  WHERE 
  {
    wd:Q21011427 wdt:P527 ?player .
    OPTIONAL { ?player wdt:P569 ?birthday }.
    OPTIONAL { ?player wdt:P27 ?nationality }.
    OPTIONAL { ?player wdt:P1618 ?number } . 
  
    SERVICE wikibase:label {
      bd:serviceParam wikibase:language "de" .
    }
  } group by ?player