The filter comes with the text domain as second argument. So you could do this:
function wpdev_170138_plugin_locale( $locale, $domain ) {
if ( $domain === 'myplugin' ) {
return get_option( 'jezik' );
}
return $locale;
}
add_filter( 'plugin_locale', 'wpdev_170138_plugin_locale', 10, 2 );
Now only your plugin’s locale is changed.