Localization - How do we manage multilingual, multi-environment on multiple domains?
You have one Craft install and one DB. Do everything described in that article, just replace the subfolder paths with the different domains:

return array(
    // ...
    'siteUrl' =&gt; array(
        'en' =&gt; 'http://example.com/',
        'es' =&gt; 'http://example.es/',
    ),
);


Then all you have to do is to configure your webhost so that it routes those domains to different index.php files. It should contain the info about the locale and point to Craft folder:

// Path to your craft/ folder
$craftPath = '../../craft';

// Tell Craft to serve the Spanish site
define('CRAFT_LOCALE', 'es');