Examples:
https://meta.wikimedia.org/wiki/Special:NoticeTemplate/view?template=FDCpropreview20132v2&wpUserLanguage=s causes a "Wikimedia Foundation Error" with the following message":
"PHP fatal error in /usr/local/apache/common-local/php-1.21wmf12/includes/cache/MessageCache.php line 630:
Call to undefined method languages::getCode()"
https://en.wikipedia.org/w/index.php?uselang=s yields a page with the following text:
[6855416c] 2013-03-30 01:00:28: Fatal exception of type MWException
Version: unspecified
Severity: normal