Regional settings are not real regional settings, because MediaWiki doesn't have a concept of region. It only has languages.
That means, although they usually apply to several languages, or they may vary between various regions in the world using a common language, these settings need to be set once and only once per language as far as our work here is concerned. Individual wikis can later change their settings for themselves, however.
Time and date formats
- Time and dates are shown on special pages and alike. The default time and date format is used for signatures, so it should be the most used and most widely understood format for users of that language. Also anonymous users see the default format. Registered users can choose other formats in their preferences. If you are familiar with PHP's time() format, you can try to construct formats yourself. MediaWiki uses a similar format string, with some extra features. If you don't understand the previous sentence, that's OK. You can provide a list of examples for developers. Just make a request on the support page. Be prepared to answer questions about minor details.
TODO: write something
- When a wiki page is being edited, and a user has allowed it in his or her Special:Preferences, a set of icons is displayed above the text area where one can edit. The toolbar buttons can be set  but there are no messages for it. What we need is a set of properly sized
.png files. Plenty of samples can be found in Category ButtonToolbar of Wikimedia Commons, and there is an empty button image to start off from.
If you need the buttons altered for a language, and you have the proper images together, ask a developer to upload them, or make a request on the support page. Note, this can only be done when your language is already in the MediaWiki svn, which usually means a good portion of its messages have been translated, otherwise you must just wait, and have it done later.