Suppose there are two wikis: wiki 1 and wiki 2.
Both wikis share the same cluster.
Search for any string in Special:SearchTranslations(wiki 1) that exist in both wikis.
Message groups of wiki 1 is listed but not of wiki 2.
Expected: It should list both the wikis message groups
The problem is that MessageGroups::getGroupStructure(); returns aggregate groups for only wiki 1 (relation between group and subgroups) and do not know anything about wiki 2. Since translations for wiki 2 exist in the shard, It would be possible to list filtered message groups but don't know of any possible way to map groups and subgroups relationship.