Bei rofro's solution bedient und ein bißchen angepasst. Bis jetzt scheint alles so zu funktionieren wie es soll.

/wiki/LocalSettings.php:

$wgScriptPath       = "/wiki";
$wgScript           = "$wgScriptPath/index.php";
$wgRedirectScript   = "$wgScriptPath/redirect.php";
 
## If using PHP as a CGI module, use the ugly URLs
$wgArticlePath      = "$wgScriptPath/$1";

/wiki/.htaccess:

RewriteEngine on
 
# Verifying if user forgot to put trailling slash. If so, we'll rewrite to Main_Page
RewriteCond %{REQUEST_URI} ^/wiki$
RewriteRule ^(.*) /wiki/index.php?tile=Main_Page [L]
 
# Don't rewrite requests for files in MediaWiki subdirectories,
# MediaWiki PHP files, HTTP error documents, favicon.ico, or robots.txt
RewriteCond %{REQUEST_URI} !^/wiki/docs/
RewriteCond %{REQUEST_URI} !^/wiki/extensions/
RewriteCond %{REQUEST_URI} !^/wiki/images/
RewriteCond %{REQUEST_URI} !^/wiki/includes/
RewriteCond %{REQUEST_URI} !^/wiki/languages/
RewriteCond %{REQUEST_URI} !^/wiki/maintenance/
RewriteCond %{REQUEST_URI} !^/wiki/math/
RewriteCond %{REQUEST_URI} !^/wiki/skins/
RewriteCond %{REQUEST_URI} !^/wiki/tests/
RewriteCond %{REQUEST_URI} !^/wiki/(redirect|texvc|index).php
 
# Make sure there is no query string (Unless user is making a search)
RewriteCond %{QUERY_STRING} ^$ [OR] RewriteCond %{REQUEST_URI} ^/wiki/Special:Search
 
# Rewrite http://wiki.domain.tld/article properly, this is the main rule
RewriteRule ^(.*) /wiki/index.php/$1 [L,QSA]