I would like to structure my url in the .htaccess
as follows https://exmaple.com/index.php?lang=de-DE&path=/dir/subdir/
to https://example.com/de-DE/dir/subdir/
but keep ability to add additional GET-Parameter.
For the directory i tried this but didn't work out
RewriteEngine On
RewriteRule /(.+)$ /index.php?path=$1 [L,QSA]
Based on your shown samples, could you please try following. Please make sure you clear your cache before testing your URLs.
RewriteEngine ON
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^/]*)/([^/]*)/?$ index.php?lang=$1&path=$2 [L]
OR as per OP's comment use QSA flag along with L
flag to append previously passed query string to newly build one in above rules.