Add main Wikimedia extensions and Translate to localisation stats

https://translatewiki.net/wiki/Translating:Group_statistics
All Wikimedia extensions + core is half of all MediaWiki, quite useless.
Translate because we need to show how many languages TWN is in.
Flagged Revs is probably not interesting any longer but not removing it here.

Should be useful also for LangCom after the change to policy:
<https://meta.wikimedia.org/w/index.php?title=Talk:Language_proposal_policy&oldid=5328450#Update_to_policy>
See talk page for new proposed stats; how outdated is the "core most used" list?

While at it, added some more (in)formal variants for consistency.
I'm unsure about the criteria for things like crh-cyrl/crh-latn.

Change-Id: I2f13b1fce961357b8642bb078f572534397ab7a7
Merge "Add main Wikimedia extensions and Translate to localisation stats"