Great Andi!
My .htaccess is now:
## Enabble this to restrict editing to logged in users only
#disable indexes
Options -Indexes
## make sure nobody gets the htaccess files
<Files ~ "^[\._]ht">
Order allow,deny
Deny from all
Satisfy All
</Files>
RewriteEngine on
RewriteBase /wiki
RewriteRule ^_media/(.*) lib/exe/fetch.php?media=$1 [QSA,L]
RewriteRule ^_detail/(.*) lib/exe/detail.php?media=$1 [QSA,L]
RewriteRule ^_export/([^/]+)/(.*) doku.php?do=export_$1&id=$2 [QSA,L]
RewriteRule ^$ doku.php [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule (.*) doku.php?id=$1 [QSA,L]
And everything works fine!
Thank you so much for your help!
Markus