Wikimedia Bugzilla is closed!

The used MediaWiki localization for users not logged on or creating accounts (= no language set manuallly in the user settings) in german language countries currently always is 'de', regardless if the browser locale is 'de', 'de-DE', 'de-CH' or 'de-AT' or form which country the IP address is.

Suggestions:

1) the locale 'de-at' should be used if the browser reports 'de-AT'. 
2) the locale 'de-ch' should be used if the browser reports 'de-CH', 'de-LI', 'fr-CH', 'it-CH' (fr and it because the number formats are the same in de-CH and readers with german language knownledge there uses the rules of Switzerland and not of Germany).

If the browser reports any other locale (or 'de', 'de-DE'): fallback to 'de'.