sitemap.xml with polylang

Hi there

probably the easiest question ever, but I couldn’t fix it. I have a wordpress site with 3 languages. For the time being I just want the sitemap in the root folder, but it ends in this url:
http://www.koenig-ascona.ch/index.php?xml_sitemap=params=.
If I run any SEO-checker to have my page checked, they can’t find the sitemap. I tried to follow your instructions about moving it in the root folder, but somehow it didn’t work, not sure if I entered the old subfolder correctly in the htaccess code:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^sitemap(-+([a-zA-Z0-9_-]+))?\.xml(\.gz)?$ /index.php?/sitemap$1.xml$2 [L]
</IfModule>

Any suggestions?

Thanks
Manuel