[out:xml][timeout:3600]; ( relation(10985766)['wikipedia'='de:Ölbach (Wiembach)']; way(949060309)['wikipedia'='de:Naturschutzgebiet Sürthtal (Kürten)']; ); (._;>;); out meta qt;//['wikipedia tag links to 404']
[out:xml][timeout:3600]; ( relation(12795178)['wikidata'='Q47498444']['wikipedia'='de:Naturschutzgebiet Naafbachtal']; relation(12796666)['wikidata'='Q56557783']['wikipedia'='de:Wahner Heide']; way(123462771)['wikidata'='Q61896510']['wikipedia'='de:Altes Schloss Bensberg']; way(217994693)['wikidata'='Q15814506']['wikipedia'='de:Liste der Baudenkmäler in Rösrath']; ); (._;>;); out meta qt;//['wikipedia wikidata mismatch']
[out:xml][timeout:3600]; ( way(231134701)['wikipedia:fixme'='Su 9:45']; ); (._;>;); out meta qt;//['invalid old-style wikipedia tag']
[out:xml][timeout:3600]; ( node(399430453)['information'='board']['wikipedia'='de:Heerweg Köln–Dortmund']; ); (._;>;); out meta qt;//['information board with wikipedia tag, not subject:wikipedia']
[out:xml][timeout:3600]; ( node(1510010687)['operator:wikidata'='Q157645']['operator:wikipedia'='en:Deutsche Post']; node(1890568651)['operator:wikidata'='Q157645']['operator:wikipedia'='en:Deutsche Post']; node(371426920)['operator:wikidata'='Q157645']['operator:wikipedia'='en:Deutsche Post']; node(6331347570)['operator:wikidata'='Q157645']['operator:wikipedia'='en:Deutsche Post']; ); (._;>;); out meta qt;//['wikipedia wikidata mismatch - for operator prefixed tags']
JOSM Wikipedia plugin
Note to self: online version hosted at https://matkoniecz.github.io/OSM-wikipedia-tag-validator-reports, files are stored at https://github.com/matkoniecz/OSM-wikipedia-tag-validator-reports.