LANG not inherited in process environment on MacOS

On Linux LANG is present in the list of environment variables returned by QProcessEnvironment::systemEnvironment().  However, on MacOS LANG is not present, as you can see from the output of QProcessEnvironment::systemEnvironment().toStringList().join('\n'):

Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.SQQgYPhgxv/Render
HOME=/Users/richard
LOGNAME=richard
PATH=/usr/bin:/bin:/usr/sbin:/sbin
SHELL=/bin/bash
SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.Ux4q7g4U0B/Listeners
TMPDIR=/var/folders/b_/xb2y4mrn2nd87ph_3tz2hsbc0000gn/T/
USER=richard
XPC_FLAGS=0x0
XPC_SERVICE_NAME=com.inviska.Inviska MKV Info.5144
 __CF_USER_TEXT_ENCODING=0x1F5:0x0:0x2

Running "printenv LANG" in a MacOS console returns "en_GB.UTF-8", so LANG is definitely defined in the system environment.  You would therefore expect it to be inherited in the process environment, which on Linux it is, but on MacOS it isn't.

The documentation for QProcessEnvironment::systemEnvironment() says, "The systemEnvironment function returns the environment of the calling process."  LANG is defined in the calling process, but isn't being returned by systemEnvironment(), so there is an issue where that function isn't doing what the documentation says.

The absence of LANG in the process environment can also create problems when running a program in a QProcess.  For example, the MKVToolNix command line tools do not function correctly if LANG is not defined, so if you run it in a QProccess on MacOS it doesn't work properly.  You therefore have to manually define LANG with QProcess::setEnvironment().

A process would normally inherit the parent processes environment variables, but with Qt on MacOS that doesn't seem to be happening.