In the Navigation Panel, the German umlauts are sorted after Z

After discussion with other devs, we concluded that we need to:

develop a mechanism to dynamically modify the queries when they're loaded (https://github.com/xwiki/xwiki-platform/blob/f34d6bb28caf7f862eb5d98ea844b734924a8865/xwiki-platform-core/xwiki-platform-index/xwiki-platform-index-tree/xwiki-platform-index-tree-api/src/main/java/org/xwiki/index/tree/internal/nestedpages/query/QueryRegistrationHandler.java#L71-L85 ) to add a collation that could be configured in xwiki.properties.