query: SELECT ?item ?itemLabel ?authorLabel ?languageLabel WHERE {
    ?item wdt:P31 wd:Q3331189.
    ?item wdt:P921 wd:Q1852569.
    OPTIONAL {?item wdt:P50 ?author}.
    OPTIONAL {?item wdt:P407 ?language}.
    SERVICE wikibase:label {bd:serviceParam wikibase:language "cs,en"}
  }