The user’s locale, in the format `language[_territory][.
codeset][modifier]`, where `language` is an ISO 639 language code, `territory` is an ISO 3166 country code, and `codeset` is
a character set or encoding identifier like `ISO-8859-1` or `UTF-8`; as specified by [`setlocale(3)`](man:setlocale(3)).
The locale may be the empty string, which means the user is using the system default locale.
The property may be null if it wasn’t possible to load it from the daemon.