Would it be possible to write a bot which simply goes through all the
pages, following all the interwiki links that currently exist and
placing them where they don't exist? This seems like it would be very
easy for someone to write, easy to implement, and very effective.
For example, if an article on EN links to an article on ES, but that one
links to an article on DE, then the bot will go back through and add
es/de to en, en/de to es, and es/en to de, etc.
This would eliminate a lot of the problems encountered by the Interwiki
Link Checker, for example, which can't deal with comparing English and
Chinese (provided that at least one page somewhere in the chain links to
the Chinese version).
Of course, it isn't a complete solution, but it seems like it would be a
very effective one. For any chains where there are discrepancies (en ->
de -> a different en), it can just not bother with that chain.
brian0918