Special:LanguageStats is extremely cluttered on Meta-wiki and might become so on other wikis in the future. That page being slow and cluttered, turns unusable for translators (not to mention stats update problem as described in T160565)
Currently there is an aggregate group "Affiliates". And there are aggregate groups like "Wikimedia France", "Wikimedia Chile", "Wikimedia Russia" etc, which should become subgroups of the "Affiliates" parent group. Also all the "Grants:..." aggregate groups should go to a single parent "Grants" aggregate group.
"2015 Community Wishlist Survey" and "2016 Community Wishlist Survey" should go to "Community Wishlist Survey" parent group, and so on.
I think this will solve the cluttering problem, but it would be nice to make Special:AggregateGroups work faster, if it is possible at all.
I'm thinking of a system like on Translatewiki.net – the "MediaWiki" aggregate group has a subgroup of "MediaWiki extensions", which itself contains three more subgroups. But perhaps you might invent something even more convenient.