Wikimedia has made an amazing UI for translating wiki articles, Content Translation, which uses Apertium to provide paragraph-level suggestions for post-editing.
See also Wikipedia_dumps for how to use published translations to improve your Apertium translator.
 How to use it on your own wiki
 Content Translation's format handling
CT has some workarounds for issues with Apertium's HTML Format handling, see
The CT code that does this is in https://github.com/wikimedia/mediawiki-services-cxserver/blob/master/lib/mt/MTClient.js#L139 (it might be nice one day to extract that into a standalone tool? see also Reordering superblanks )