You can take part in DocBook discussion by subscribing to the DocBookAppsMailingList and the DocBookMailingList and by tuning into the DocBookIrcChannel. Before posting to either of the mailing lists, make sure to read the guidelines.
For Spanish users they have a help-forum.
There is also DocBook mailing list in the Czech language mailto:email@example.com. You can subscribe to it by sending e-mail message to mailto:firstname.lastname@example.org, list is also accessible as news group cz.comp.text.docbook.
For German speaking users there is a German language DocBook mailing list. There is a list information page http://placebo.hpi.uni-potsdam.de/mailman/listinfo/docbook, where you can subscribe and a archive http://placebo.hpi.uni-potsdam.de/pipermail/docbook/ of recent posts.