In T216322: Create a new namespaces on thai wikimedia projects a new namespace วิกิเยาวชน was created for thwikibooks, but there are still talk pages with this prefix. That is invalid in mediawiki
MariaDB [thwikibooks_p]> select count(*) from page where page_namespace = 1 and page_title like 'วิกิเยาวชน:%'; +----------+ | count(*) | +----------+ | 37 | +----------+ 1 row in set (0.002 sec)
https://th.wikibooks.org/?curid=11436&uselang=en&action=edit
works, but clicking "View history" gives
https://th.wikibooks.org/w/index.php?title=%E0%B8%9E%E0%B8%B9%E0%B8%94%E0%B8%84%E0%B8%B8%E0%B8%A2:%E0%B8%A7%E0%B8%B4%E0%B8%81%E0%B8%B4%E0%B9%80%E0%B8%A2%E0%B8%B2%E0%B8%A7%E0%B8%8A%E0%B8%99:%E0%B9%80%E0%B8%A5%E0%B8%82%E0%B8%95%E0%B8%B1%E0%B8%A7%E0%B9%80%E0%B8%A5%E0%B9%87%E0%B8%81/8&action=history&uselang=en
and shows error "The requested page title refers to a talk page that cannot exist."