Try typing a URL with a page parameter that has an invalid title character, for example page=Hel}lo.
In production Wikipedia this produces Exception encountered, of type "BadMethodCallException".
On my local machine, this produces a blank page and the server log says: PHP Fatal error: Call to a member function getDBkey() on null in /home/amire80/dev/livowiki/extensions/ContentTranslation/specials/SpecialContentTranslation.php on line 69
Unless a URL is typed manually, this is unlikely to actually happen because the page selector validates the titles, but should probably be handled.
A similar frontend issue: T111544.