I’d propose to add a list of substitutes for special characters (like äöü and these accent chars) into the langfiles. That would allow langfile maintainers to select appropriate substitutes for these characters, in case they’re used as an alias or somewhere else where only basic ASCII is allowed. This makes especially sense for the automated alias generation from pagetitle.
Maybe this way:
$_lang['char'][196] = 'Ae'; // 'Ä'
