I've been getting this error on a test wiki I have the latest 1.18 checked out on. The error shows up when I visit the edit page.
Warning: Invalid argument supplied for foreach() in /languages/Language.php on line 423
Note that this test wiki has CACHE_NONE set since I'm developing. That could be related to the situation where that error shows up.
Version: 1.18.x
Severity: normal