update .htaccess file and 500 error occurs

Frustrated and hoping for a fresh look at this.
I have followed the instructions to the T from the codex ebook.
All is fine until I replace the code given into my .htaccess file.
If I remove the file then I can log in butwith the file there I get a 500 server error. I have spend a few hours now reading blocgs and tips and they all seem to point to different issues.
I am on an Apache Linux server with 1and1 which seems to be problomatic with this type of mod-rewrite – what I have read a number of times but tried all those tips and still no luck. I must have rewritten this file about 25 times now.
Not sure if this makes a difference but the wordpress install is located like this. ftp://[email protected]/en I think this may the error but am not sure.

This is current code in .htaccess file.

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L][L]

Please some one help. Thanks.