Hi!
Extracting information from mediawiki can be done using severals ways: using prebuilded tools, programming scripts, using database dumps and others.
So, the main question is: what mediawiki do you need replcate? DO you need replicate some articles? do you need replicate an full mediawiki site?
The other questions is.. do you have an mediawiki instance working?
Be advice because some mediawiki admins restricted access for avoid heavy loads on mediawiki sites.
I've worked with mediawiki from long time ago installing it without problems.
Open to questions,