You can either build the Xtra yourself (see below), or download a pre-built version it from the l4a-releases, and extract it. Once done, you can open the Xtra, which will be sent to Adium for installation.
(The path shown assumes you built the Xtra.)
You then need to restart Adium, and make sure this new Plugin is enabled in the Xtras manager.
You should be able to enable carbons for a Jabber account by entering
in any chat window to enable carbons for this account.
You should similarly be able to interact with lurch and enable OMEMO through
lurch command. See
for more details.
On Using Libpurple Plugins in Adium
The plugin boilerplate comes from the Adium Tutorial adium-plugin-tutorial, which still seems to be relevant as of Sierra (10.12.4)/Xcode 8.3.2.
One notable difference, is, however, that libpurple plugins need to use the
AdiumLibpurplePlugin wrapper extension, so the
loadLibpurplePlugin methods of the
AILibpurplePlugin class are called.
The XCode GUI tools are needed. You can get them from the AppStore xcode-appstore after having sold your soul and given banking details. Apart from that, it's free-as-in-beer.
You then need to agree to lease out your first born as a receptacle for Steve Jobs' soul. This is done as follows.
sudo xcodebuild -license
Will fetch the necessary third-party sources, and build them.