If/When you want to have wordpress in your own language you could/should download the swedish version imho.
Go and look here for the translated package. Because thats the best way to do.
Only having some language files doesn’t do always the trick.
Download the package from the link I mentioned, unzip/untar unrar or whatever you do/want and just overwrite it through ftp.
Don’t worry it wont overwrite any of your settings made in wp-config.php (because it has not even a wp-config.php!). Settings you may have made in core-files will be lost but that would always happen at updates if done. Neither will it “kill” your childtheme(s) or whatever. And if you already have define('WPLANG', 'sv_SE'); in wp-config.php then your good to go.
About wp native dashboard (the plugin) is only for you as user/admin to see and not for your visiters (Till they login and make the setting in backend themselves). Btw I love that plugin because my native is different from my wordpress language we use and works flawless.(We use Version 1.3.12 & WP3.71 without any problems)
When it brakes your wordpress you could/should check if wordpress has other problems (just as reminder if a plugin not works or maybe (worse case) brakes your wordpress, it is not always that plugin but can also be a combination with other plugins)
To activate debug go to wp-config.php and change setting to define( 'WP_DEBUG', true );
A little helpfull code we use is following (Only have to set true or false in the first code line)
define( 'WP_DEBUG', true ); // Or false
if ( WP_DEBUG ) {
define( 'WP_DEBUG_LOG', true ); // writes errors down in wp-content/debug.log
define( 'WP_DEBUG_DISPLAY', true );
}
You could create the logfile (debug.log) yourself by hand in folder wp-config, be aware that it shows a lot and don’t forget to disable it after all is working again.
(We work offline, in a sandbox, and always test with debug activated to be sure that it has online no issues).