Thanks for bringing that up to our attention, it is indeed a forgotten
place!. also thanks for that table, it should help. but as you said,
simple welcoming message is essential concentrating on the most
important aspects. and yes, yours are designed specifically for commons
place as it seems. especially the 'how to' change language. another
thing, you should include a semi-protected template in
MediaWiki:Welcomecreation page. as I have seen, a lot of registered
users can be creative and yields great results.
Mohamed Magdy