fwiw, my experience today trying to tell a community about a change we made:
we enabled WebFonts for my.wp:
https://gerrit.wikimedia.org/r/#/c/20727/1/wmf-config/InitialiseSettings.php
as requested in https://bugzilla.wikimedia.org/show_bug.cgi?id=34817
because it was assigned to me in Gerrit and looked like an easy change. So after merging and pushing out to cluster..
first i joined the IRC channel #wikipedia-my . It was empty.
Then i checked for a mailing list. It did not exist.
Then i went to the Wiki looking for the right place to drop a message.
I do not speak their language, actually i don't even have the right fonts installed:
http://my.wikipedia.org/wiki/Special:RecentChanges
I just tried Village_Pump, http://my.wikipedia.org/wiki/Wikipedia:Village_Pump but it appears empty afaict.
At this point i gave up and relied on the comment in Bugzilla being enough..
The last part took waaaay longer than the actual merge of course.
If i could have a matrix with links please, one for every project in every language with just the right places to leave comments on, i would more often do this...