New WP installation due to language issues

There isn’t really a Swedish version of WordPress although they do provide a convenient package that has the language files already loaded. The only differences from the core (English) distribution are the folder wp-content/languages, the variable $wp_local_package="sv_SE"; set in wp-includes/version.php, the localized readme.html file and the wp-config-sample.php file.

So yes, you should be safe uploading directly on top of your current install as long as you upload the same version number (3.9.2 to 3.9.2 or 3.9.1 to 3.9.1).

The file wp-config-sample.php has PHP comments localized to your language so you can either update the variables in that file from your current wp-config.php and just rename it or you can just set define('WPLANG', 'sv_SE'); in your current config file if your fine with comments in English.