newmessageslinkplural and newmessagesdifflinkplural (introduced in I8870111802 to fix bug 12701) both have a single parameter, that one could expect to be the number of or (respectively) messages or changes. However, this parameter can only take values of '1' (when there's one message/change) or '2' (when there are more). While this behavior is documented, it's obviously confusing, and I just had to fix translations of these messages to Polish.
As I assume obtaining correct values is impossible (too database-intensive?), both messages should be split into two – one for singular and one for plural form. If this is considered such a very bad practice, then at least we should usea different value than '2' to make errors in translations more obvious – '999' would do.
Whiteboard: gci2013 https://www.mediawiki.org/wiki/Google_Code-In#Candidate_tasks