it talks about
Maybe extending the ruleset XML Schema to be able to configure per-language options such as these?
what would be the correct way to do this?
the pmd maven plugin requires that I explicitly specify pmd-core with pmd-java as dependencies for it to work.
That's because m-pmd-p by default supports java, so has in any case the dependency for pmd-java. If you now override the plugin-dependencies, you can only add additional dependencies (like pmd-xml), but never remove (or exclude). Therefore you need to make sure, to use the same pmd version or you need to override all pmd dependencies (that the m-pmd-p already has) with the same version. A mix between different versions of different pmd modules is not supported.