Last modified: 2014-02-18 11:59:26 UTC
Draw a diagram or something of the possible translation state changes and define what each of those should do. That should eliminate lots of bugs that can be there just because we did not consider all of the possibilities and leave only genuine bugs left.
Example of a case we do not seem to handle currently: https://www.mediawiki.org/wiki/Thread:Help_talk:Extension:Translate/Outdated/Fuzzy