http://pubs.opengroup.org/onlinepubs/9699919799/
  The Open Group Base Specifications Issue 7
  IEEE Std 1003.1, 2013 Edition

[1]
When no formatting operand is specified, the output in
the POSIX locale shall be equivalent to specifying:
  date "+%a %b %e %H:%M:%S %Z %Y"


FreeBSD 11.0-BETA3
==================

$ LC_ALL=C date
Fri Aug  5 15:20:25 CEST 2016
  (ok, same as in 10.3)

$ LC_ALL=C date '+%a %b %e %H:%M:%S %Z %Y'
Fri Aug  5 15:20:25 CEST 2016
  (ok, same as in 10.3)

$ LC_ALL=en_US.UTF-8 date
Friday, August  5, 2016 at 03:20:25 PM CEST
  (breaks posix [1], breaks compatibility with 10.3!)

$ LC_ALL=en_US.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
Fri Aug  5 15:20:25 CEST 2016
  (ok, same as in 10.3)

$ LC_ALL=es_ES.UTF-8 date
 5 de agosto de 2016, 15:20:25 CEST
  (breaks posix [1], missing day of the week name!)

$ LC_ALL=es_ES.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
vie. ago.  5 15:20:25 CEST 2016
  (ok, different from 10.3 (dots))

$ LC_ALL=it_IT.UTF-8 date
venerdì  5 agosto 2016 15:20:25 CEST
  (breaks posix [1], different from 10.3 (long names))

$ LC_ALL=it_IT.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
ven ago  5 15:20:25 CEST 2016
  (ok, different from 10.3 (case changed))

$ LC_ALL=fr_FR.UTF-8 date
vendredi  5 août 2016 15:20:25 CEST
  (breaks posix [1], different from 10.3 (long names))

$ LC_ALL=fr_FR.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
ven. août  5 15:20:25 CEST 2016
  (ok, different from 10.3 (dots))


FreeBSD 10.3-RELEASE-p6
=======================

$ LC_ALL=C date
Fri Aug  5 15:15:11 CEST 2016
  (ok)

$ LC_ALL=C date '+%a %b %e %H:%M:%S %Z %Y'
Fri Aug  5 15:15:11 CEST 2016
  (ok)

$ LC_ALL=en_US.UTF-8 date
Fri Aug  5 15:15:11 CEST 2016
  (ok)

$ LC_ALL=en_US.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
Fri Aug  5 15:15:11 CEST 2016
  (ok)

$ LC_ALL=es_ES.UTF-8 date
viernes,  5 de agosto de 2016, 15:15:11 CEST
  (breaks posix [1])

$ LC_ALL=es_ES.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
vie ago  5 15:15:11 CEST 2016
  (ok)

$ LC_ALL=it_IT.UTF-8 date
Ven  5 Ago 2016 15:15:11 CEST
  (breaks posix [1])

$ LC_ALL=it_IT.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
Ven Ago  5 15:15:11 CEST 2016
  (ok)

$ LC_ALL=fr_FR.UTF-8 date
ven  5 aoû 2016 15:15:11 CEST
  (breaks posix [1])

$ LC_ALL=fr_FR.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
ven aoû  5 15:15:11 CEST 2016
  (ok)


OSX version 10.9.5
==================

$ LC_ALL=C date
Fri Aug  5 14:57:14 CEST 2016
  (ok)

$ LC_ALL=C date '+%a %b %e %H:%M:%S %Z %Y'
Fri Aug  5 14:57:14 CEST 2016
  (ok)

$ LC_ALL=en_US.UTF-8 date
Fri Aug  5 14:57:14 CEST 2016
  (ok)

$ LC_ALL=en_US.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
Fri Aug  5 14:57:14 CEST 2016
  (ok)

$ LC_ALL=es_ES.UTF-8 date
viernes,  5 de agosto de 2016, 14:57:14 CEST
  (sames as in 10.3, breaks posix [1])

$ LC_ALL=es_ES.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
vie ago  5 14:57:14 CEST 2016
  (ok)

$ LC_ALL=it_IT.UTF-8 date
Ven  5 Ago 2016 14:57:14 CEST
  (breaks posix [1], sames as in 10.3)

$ LC_ALL=it_IT.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
Ven Ago  5 14:57:14 CEST 2016
  (ok)

$ LC_ALL=fr_FR.UTF-8 date
Ven  5 aoû 2016 14:57:14 CEST
  (breaks posix [1], similar to 10.3 (but case change))

$ LC_ALL=fr_FR.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
Ven aoû  5 14:57:14 CEST 2016
  (ok)
 

Fedora Linux 4.6.4-301.fc24.x86_64
==================================

$ LC_ALL=C date
Fri Aug  5 15:10:40 CEST 2016
  (ok)

$ LC_ALL=C date '+%a %b %e %H:%M:%S %Z %Y'
Fri Aug  5 15:10:40 CEST 2016
  (ok)

$ LC_ALL=en_US.UTF-8 date
Fri Aug  5 15:10:40 CEST 2016
  (ok)

$ LC_ALL=en_US.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
Fri Aug  5 15:10:40 CEST 2016
  (ok)

$ LC_ALL=es_ES.UTF-8 date
vie ago  5 15:10:40 CEST 2016
  (ok)

$ LC_ALL=es_ES.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
vie ago  5 15:10:40 CEST 2016
  (ok)

$ LC_ALL=it_IT.UTF-8 date
ven  5 ago 2016, 15.10.40, CEST
  (breaks posix [1])

$ LC_ALL=it_IT.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
ven ago  5 15:10:40 CEST 2016
  (ok)

$ LC_ALL=fr_FR.UTF-8 date
ven. août  5 15:10:40 CEST 2016
  (ok)

$ LC_ALL=fr_FR.UTF-8 date '+%a %b %e %H:%M:%S %Z %Y'
ven. août  5 15:10:40 CEST 2016
  (ok)


Debian 8.0 / Linux 4.4.16-v7+
=============================

$ LC_ALL=C date
Fri Aug  5 15:25:49 CEST 2016
  (ok)

$ LC_ALL=C date +%a %b %e %H:%M:%S %Z %Y
Fri Aug  5 15:25:49 CEST 2016
  (ok)

$ LC_ALL=en_US.UTF-8 date
Fri Aug  5 15:25:49 CEST 2016
  (ok)

$ LC_ALL=en_US.UTF-8 date +%a %b %e %H:%M:%S %Z %Y
Fri Aug  5 15:25:49 CEST 2016
  (ok)

$ LC_ALL=es_ES.UTF-8 date
vie ago  5 15:25:49 CEST 2016
  (ok)

$ LC_ALL=es_ES.UTF-8 date +%a %b %e %H:%M:%S %Z %Y
vie ago  5 15:25:49 CEST 2016
  (ok)