Run localized WordPress sites easily. Select the language and everything else happens automatically.
WordPress Language lists all the languages that appear in the WordPress Translation project. If your language is not listed, it just doesn't have official WordPress translation.
WordPress Language downloads the official translations from the WordPress localization project. These are the same translations used to create the localized WordPress downloads.
No. WordPress Language only downloads the existing translations from the WordPress Translation project.
The plugin detects new changes and will offer you to update the translation. Of course, that depends on the translation actually being available.
No. WordPress Language sets one single language for your site. For multilingual sites, have a look at WPML.