[out:xml][timeout:3600]; ( relation(6858088)['wikipedia'='de:Wallburg Engelskirchen']; ); (._;>;); out meta qt;//['wikipedia tag links to 404']
[out:xml][timeout:3600]; ( node(10866802935)['wikidata'='Q882204']; ); (._;>;); out meta qt;//['should use a secondary wikipedia tag - linking from wikipedia and wikidata tag to a transport accident']
[out:xml][timeout:3600]; ( node(7295005165)['wikidata'='Q1498760']['wikipedia'='de:Espert']; node(7295007194)['wikidata'='Q1368200']['wikipedia'='de:Geilensiepen']; ); (._;>;); out meta qt;//['wikipedia wikidata mismatch']
[out:xml][timeout:3600]; ( node(2021476552)['wikidata'='Q865518']['wikipedia'='de:Birkenbach']; ); (._;>;); out meta qt;//['wikipedia wikidata mismatch - wikipedia points to disambiguation page and wikidata does not']
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.