WP installed is asking to install if typed domain.com

Question

I got a problem trying to access the landing page typing domain.com instead www.domain.com If I type domain.com/rus the WP goes to domain.com/rus/wp-admin/install.php

but if I type www.domain.com/rus the landing page is loaded correctly if I type any address of known pages or post without the www the pages and post are loaded correctly, the main problem is the home page.

Settings:
reading : last post - taken from index.php
WP URL: http://www.domain.es/rus
Site URL: http://www.domain.es/rus

I have other site with same information http://www.domain.es/eng and this is working perfectly, now I´m planing to have a site in rusian :) but I got this error and I don´t want to transfer 400M of images again.

NOTES:
There aren´t blank spaces in wp-config.php ( i´ve solved this issues since 4 years ago) the .htaccess shows this code same as site eng (obviusly its own /eng and /rus folder) RewriteBase /rus/
RewriteRule . /rus/index.php [L]

Answer 1

Adding this lines to .htacces solved the redirect problem to wp-admin/install.php if typed the domain.com without the www even if the WP was completely installed and settings configured properly.
RewriteCond %{HTTP_HOST} ^www.domain.com/rus [NC]
RewriteRule ^$ /index.php [NC,L]
Now I can continue with rusian translation.

The main problem was a defective plugin, which was blocking the Adminn panel and routines that checks the config file; the error on the plugin was a wrong coded lines with non UTF-8 Format.