The DumpHTML extension looks like it's in a pretty bad state, it doesn't
work at all in the current version of MediaWiki.
This seems to be an unfortunate symptom of how it's used and how it's
treated by core developers.
DumpHTML is most useful when someone is shutting down and archiving
their wiki, so it doesn't get tested regularly.
The act of creating a version of wiki pages suitable for offline use
from static files is something which inherently requires different
behaviour from things deep within core.
Because DumpHTML has been segregated into an extension and core doesn't
support an offline/dump mode internally DumpHTML has to use a bunch of
hacks to make core behave properly during the dump.
Then, because they are completely unaware of DumpHTML's needs, core
developers make improvements to core that then break DumpHTML without
providing it an alternative interface to get what it needs out of core.
For one DumpHTML needs to proxy and mess with file repo behaviours. To
do that it messed with properties like thumbScriptUrl, but then those
properties were protected leaving DumpHTML unsupported.
This was reported as a bug a month ago, which has gone relatively unnoticed:
It also subclassed RepoGroup and since it proxied existing repo
instances instead of working with repo info it had to bypass the
__constructor. But then a $repoGroup->cache was added to the
__constructor in core, breaking DumpHTML in another way.
There are probably more issues that I haven't found yet while trying to
workaround the other issues.
~Daniel Friesen (Dantman, Nadir-Seen-Fire) [http://danielfriesen.name/