The Monobook skin hardcodes first letter lower case for certain UI-messages (CSS: .portlet h5, .portlet h6). This is a bad idea considering languages that use upper case a lot in order to differentiate different words and meanings. German is probably the most common example for such a language.

As long as you use a monolingual (German) wiki a hackish solution works; see MediaWiki:Monobook.css/de in your wiki of choice for the CSS code which works on wikis with German as default language only.

As CSS files can't be (and shouldn't need to be) localisable using the sub page style the solution doesn't work in mutilingual wikis as you need to overwrite MediaWiki:Monobook.css with said code and now people of all other languages complain that their interface strings are upper case. This is due to the fact that every interface string affected by the  ".portlet h5, .portlet h6"-rule is written in any language with upper case in the UI message files.

So the solution is: Drop the forced lower case in Monobook and if you don't like your UI strings starting with upper case in your language of choice make these strings lower case right from the start in vanilla MediaWiki.

It is bad in any skin to rely on global lower case/upper case behaviour as this is not language independent. And of course Monobook is the default for the large majority. So it is a bit strange forcing the majority of users into non-standard language display because of that.

So if someone thinks that some (older) non-default skins shall use in any case upper case, please insert in these skins a force-upper-case CSS definition. At least it would hurt way less people than the current scheme.

Arnomane

P.S.: See also this post in the initial thread covering this topic: http://lists.wikimedia.org/pipermail/wikitech-l/2007-January/029275.html