RewriteEngine On
RewriteBase /
RewriteRule ^W/$ w/index.php/Main_Page [L,QSA]
RewriteRule ^wiki$ w/index.php?title=Main_Page [QSA]
RewriteRule ^wiki/$ w/index.php?title=Main_Page [QSA]
RewriteRule ^wiki/(.*)$ w/index.php?title=$1 [QSA]