I just recently started to play with interwiki.py (Pywikipedia bot framework) for propagating interwiki links. My interest comes from organizing the category tree, so I'm focusing on interwiki links between categories. Interwiki bots normally run in autonomous mode, but this means they give up on complicated cases.
If I run this script under manual supervision, without the "-autonomous" option, it stops and asks me how to resolve each conflict. This happens ever so often. I have now (manually) sorted out the interwiki links between all languages of Category:Knowledge, which was intertwined with Category:Science, and Category:Austrian writers which was mixed up with Category:Austrian literature. Such mistakes easily happen, of course. Who can spot errors in all these languages?
Many languages had interwiki links from their category for Austrian writers to the Japanese category for Austrian literature. I'm not sure exactly when or where this error originated. But on June 19, 2007, the English and Spanish Wikipedia's interwiki link to Japanese changed from Austrian novelists to Austrian literature, i.e. from one error to another. Ten days later, this link was copied to the Dutch Wikipedia. The error was corrected on en.wikipedia on October 1, 2007, but remained on other languages. Yes, that's 15 months ago.
The circular interwiki link structure from en:Category:Austrian writers to es:CategorÃa:Escritores de Austria to ja:... and back to en:Category:Austrian literature is such a conflict that makes interwiki.py give up when it runs in autonomous mode.
Thus, corrections (as on October 1) do not propagate. Instead a report about the conflict is given in a logfile, but apparently nobody had fixed this problem in the last 15 monhts. This conflict also blocked new interwiki links from propagating.
After I cleared up the mess, 21 new interwiki links were added to the category on the Russian Wikipedia (one where I have a bot flag). That means 21 languages of Wikipedia had created categories (or announced them to the interwiki system) for Austrian writers in the last 15 months, and they all added their interwiki link to the English Wikipedia. But these additions did not propagate because of the conflict.
So, my question:
Has anybody mapped exactly how many such interwiki conflicts we have? Or how many interwiki sets do we have without conflicts? Could/should someone make a list of current conflicts and try to rank them by importance, so we can get started in fixing them?
In the longer term, we need to redesign the interwiki links into a centralized system, that can be maintained. I think the way to do this is to use Wikimedia Commons. Instead of copying all the interwiki links to every language of Wikipedia, it should be enough to add {{commons|Category:Writers from Austria}}, and the rest should happen automatically.