The general.language option is used to switch language packs. This configuration option should contain a language code for example en or sv, these codes represent XML files in the langs directory. If you want to translate the application to your language you can just duplicate on of the existing language XML files and write your own. Check this website for existing language translations.
Example of usage in the config.php file
$mcFileManagerConfig['general.language'] = "en";
Example of usage in the Web.Config file
<add key="general.language" value="en" />
Example of usage in a mc_access file
Download language package
Check this website for existing language translations.