Pidgin 2.12 has done away with a number of protocols that are no longer supported upstream, including Facebook XMPP, MSN, MySpace, Mxit, and Yahoo. Pidgin 2.12 has also restored support for AIM.
Pidgin 2.12 also has a CVE fix about out-of-bounds memory reads, fixing use of uninitialized memory, TLS certificate verification now using SHA256 checksums, and a range of other bug-fixes. There isn't much on the feature front this time around.
Details on Pidgin 2.12 can be found via the project's website at Pidgin.im.