Let's start 2013 with a fun bug.
It would be very useful when working on the skins or other bits of the interface.
Currently, to test variants handling, you have to switch the entire wiki to a language that uses variant conversion, and unfortunately it seems like all of them use non-Latin alphabets, which makes working with them considerably harder if know them than if they were in a latin script at least.
With this, you would just set $wgUsePigLatinVariant (or something similar) to true and be able to test.
Of course we could use piratey or lolcat language instead of pig latin, but it seems the nicest to me (and easier to implement).