Subversion development discussion takes place on the mailing list dev@subversion.tigris.org. You don't need to subscribe to the list just to submit a patch or two, but if you want to be involved with Subversion development on a regular basis, you should probably subscribe. It's high-traffic, but threading tends to be fairly disciplined, so you can ignore conversations you aren't interested in. For real-time chat, developers use the same IRC channel as everyone else: irc.freenode.net/svn.
The HACKING file contains developer guidelines, see:
http://svn.collab.net/repos/svn/trunk/HACKING
There you can find information about submitting patches, learning your way around the code, interacting with other developers, project governance, etc. If you don't see the answers you need there, please ask on the mailing list or in IRC, we're happy to help.
With the release of version 1.1 Subversion program output can be translated. Discussion takes place both on the Subversion development mailing list as well as dedicated native language mailing lists (l10n-??@subversion.tigris.org).
Next to any information it HACKING pertinent to translating Subversion output, additional information can be found in
http://svn.collab.net/repos/svn/trunk/TRANSLATING
Currently available translations can be found in the po section of the repository. Please contact the development mailing list when you want to start a translation not available yet.
Translations of the book "Version control with Subversion" are also actively maintained. Available languages are available at http://svn.collab.net/repos/svn/trunk/doc/translations/. Contributions can be sent to the main developers mailing list or to one of the dedicated translations lists. If you want to start a translation which is not yet available, please contact the developers mailing list to find out about the right course of action.