By default, an own config.php (configuration file) is included in the root folder of each subsite or second language. Thus, each subsite and second language is fully configurable.
Such a config.php is included in the copy templates "2lang", "2site" and "2lang2site" of the download.
If you want to run a subsite or second language in the same configuration as the main page, for example:
etc., then you simply can remove the config.php from the root folder of the subsite or second language (or rename it). After that, the appropriate subsite or second language uses the configuration file of the main installation / main site.
Now all changes to the configuration of the main installation/main site are automatically applied to all subsites and second languages without their own config.php.
In some cases this can be very convenient, especially if all the subsites and second languages are operated by the same author.