Move the interwikiSortOrders setting that is currently defined WikibaseClient.default.php from Wikibase to operations/mediawiki-config. operations/mediawiki-config should set the setting to what the default is now (the four different orders used on Wikimedia projects). The default in Wikibase for interwikiSortOrders should then be empty. The 'sort' option, which refers to an entry in interwikiSortOrders, should continue to default to 'code', which is a special value representing naive sorting by language code.
NOTE: InterwikiSorter.php currently assumes that the interwikiSortOrders has an entry called 'alphabetic'. We should get rid of that and always default to the behavior defined for sort='code'.
NOTE: sortPrepend should be unaffected by this: languages listed there always go first, in the order given.
With the two patches above merged, the code should now be agnostic to any specific sort order being defined. So the next steps are:
- define 'interwikiSortOrders' in the settings file used on the wikimedia cluster.
- make 'interwikiSortOrders' default to an empty array in WikibaseClient.default.php